Method for the treatment of dusts and concentrates
This invention relates to a method for the treatment of dusts and concentrates particularly, the invention relates to a method for the treatment of lead dusts and low lead pyritic concentrates. 
     The invention has been developed primarily for use with lead dusts and low lead pyritic concentrates and will be described hereinafter with reference to such materials. However, it will be appreciated that the invention is not limited to this particular field of use. 
     Lead dusts are a by-product of conventional lead smelting and, in the past, these dusts had to be recycled many times to recover the lead. This increased the heat load on the smelter and reduced its capacity. 
     It is an object of the present invention to provide a method of smelting lead dusts and low lead pyritic concentrates which overcomes or substantially ameliorates the problems of the prior art. 
     In accordance with the present invention there is provided a method for the treatment of a mixture of lead dusts and pyritic concentrates said method including the steps of: 
     a) feeding a mixture of lead dust and pyritic concentrate to a furnace containing molten slag; 
     b) smelting the mixture by injecting air or oxygen enriched air into the slag by means of a submerged lance to produce a lead bearing slag; and 
     c) recycling fume to the furnace. 
     Also in accordance with the present invention there is provided a method for the treatment of lead dusts, without pyritic concentrate, said method including the steps of: 
     a) feeding lead dust to a furnace containing molten slag; 
     b) smelting the dust by injecting air or oxygen enriched air into the slag by means of a submerged lance to produce a lead bearing slag; and 
     c) recycling fume to the furnace. 
     Preferably, steps a), b) and c) of both of the above aspects of the invention are continuous. 
     In a preferred embodiment, coal, coke, oil or natural gas, or any combination thereof, may be used as a fuel. 
     In a further preferred embodiment, depending upon the gangue and ash content of the feed mixture, it may be necessary to add flux to produce a fluid slag. 
     The fume is preferably recycled to the furnace via a baghouse. Most preferably, the baghouse is a dedicated unit with an integral fume return system. 
     The preferred operating temperatures range from 1150° to 1250° C. with 1170° to 1190° C. as the most preferred range. 
     Preferably, the slag will contain less than 2% sulphur and the process offgas will have an SO 2  concentration of greater than 4% to aid SO 2  recovery at an acid plant. 
     Preferably the slag will have a composition in the range 20 to 50% Pb, 10 to 20% Fe, 5 to 15% SiO 2  and 2 to 5% CaO, with typical residual impurities of up to 10% Zn, 3% Al 2  O 3  and 3% MgO. 
    
    
     A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying FIGURE, in which: 
     FIG. 1 is a process flowsheet in accordance with the method of the invention. 
    
    
     The ISASMELT process is based on submerged gas injection into melts via a top entry submerged SIROSMELT lance to produce turbulent baths in which high intensity smelting or reduction reactions can occur. 
     Lead dust, low lead pyritic concentrate, coke breeze and flux are mixed in a pug mill with sufficient water to form a moist agglomerate feedstock. The feedstock is continuously fed to a furnace by conveyor and dropped directly into a molten slag bath where it is oxidized by air injected down a lance. The slag is tapped either continuously or batch-wise and the offgas cooled by a water spray directly above the furnace, as shown schematically in FIG. 1. 
     In the following examples two feed types are considered: 
     Mix A comprised 54.7% of lead sinter plant recycle dust, 12% of lead bearing copper converter dust and 33.3% of low lead pyritic concentrate. The low lead pyritic concentrate was included to increase the SO 2  content in the offgas. 
     Mix B comprised 82% of lead sinter plant recycle lead dust and 18% of lead bearing copper converter dust. 
     The material compositions are listed in Table 1. 
     
                                           TABLE 1
__________________________________________________________________________
FEED MATERIALS USED DURING THE 250 Kg TESTWORK
                              NOMINAL CHARGE MIX
FEED MATERIALS (wt %)         Mix A         (wt %)
             Copper
                   Low Lead   54.7% Recycle Dust
                                            Mix B
Sinter Plant Converter
                   Pyritic
                          Silica
                              12% Converter Dust
                                            82% Recycle Dust
Recycle Dust Dust  Concentrate
                          Flux
                              33.3% Pyritic Concentrate
                                            18% Converter
__________________________________________________________________________
                                            Dust
Pb    32.20  30.10 13.50  --  25.72         31.82
Zn    5.10   7.60  7.60   --  6.23          5.55
Fe    8.49   1.50  24.40  1.0 12.95         7.23
Cu    1.90   2.50  2.00   --  2.01          2.01
S     12.40  13.10 33.00  --  19.34         13.53
S/SO.sub.4
      4.91   12.30 1.80   --  4.76          6.24
SiO.sub.2
      8.10   1.30  5.00   92.5
                              6.25          6.88
Al.sub.2 0.sub.3
      1.70   0.20  0.60   2.5 1.15          1.43
CaO   5.10   3.20  1.10   0.5 3.54          4.76
MgO   0.50   0.20  0.20   0.3 0.36          0.45
As    1.20   4.10  2.00   --  1.81          1.72
Sb    0.80   0.80  0.70   --  0.77          0.80
Cd    0.76   1.10  0.02   --  0.55          0.82
Bi    0.11   1.48  0.05   --  0.25          0.36
Ag (ppm)
      1520   270   4450   --  2340          1290
Au (ppm)
      31.0   trace 7.2    --  19.0          26.0
Moisture
      7.3%   14.4% 5.7%    4.0%
Proximate analysis Coke Breeze (5.5% moisture)
             86.80%
                   fixed carbon
             4.20% volatile matter
             8.59% ash
             0.46% moisture
__________________________________________________________________________
 
    
     EXAMPLE 1 
     Testwork on the lead dusts and low lead pyritic concentrates was carried out in a 250 kg ISASMELT test furnace. A total of 1780 kg of lead sinter plant recycle dust, 380 kg of lead bearing copper converter dust and 550 kg of low lead pyritic concentrate were smelted in 17 runs over 29 hours operating time. 
     The 250 kg ISASMELT test furnace has an internal diameter of 380 mm and is 1.5 m high and lined with chrome-magnesite refractories. Air is injected into the bath via a 40 mm nominal bore lance. Feed is added via a variable speed conveyor and drops directly into the molten slag bath. The offgas passes through an evaporative gas cooler and is cleaned in a reverse pulse baghouse. 
     The feed materials were mixed with coke breeze and pelletized prior to each run. Recycled fume was added during the run at a rate approximating the fume rate measured at the baghouse. Silica flux was also added to the Mix A material. 
     At the beginning of each series of runs, lead slag was fed into the furnace and melted to form a starting bath. The dust/concentrate mixture was then fed into the furnace at a controlled rate and smelted. Both normal air and air enriched to 35% O 2  were used. Oil was used as a supplementary fuel to the coke breeze. 
     During each run, slag samples were taken periodically from the furnace and the fume rates were measured at the baghouse. Operating temperatures ranged from 1150° to 1250° C., with 1170° to 1190° C. providing optimum conditions. At the conclusion of each run the slag was tapped into moulds and weighed. 
     The operating conditions and results from this testwork are tabulated in Table 2. Product assays from this testwork are given in Table 3. 
     
         TABLE 2
         AVERAGE  STARTING BATH NEW CHARGE ADDITIONS  TOTAL ACTUAL NEW
 SMELTING FINAL  Initial  MATERIAL CHARGE Dry % of New Material NOMINAL
 RUN SMELTING MATERIAL RATE BATH RUN Initial Depth (Dry %) Silica  Return M
 OISTURE TIME TIME SMELTED (kg/hr) DEPTH NUMBER Charge (mm) D &amp; L* EP**
 Cons Flux Coke Fume CONTENT (min) (min) (kg, dry) (dry) (mm)
   1 90 kg High 130 54.8% 11.2% 34.0% 4.3% 12.8% -- 13.0% 195 195 310 95
 430 Mix A Lead Slag          ie 100% 27/2/89 2 Continuing 100 54.8%
 11.2% 34.0% 4.3% 12.8% -- 13.0% 150 150 246 98 450 Mix A from Run 1
     ie 100% 27/2/89 3 70 kg Run 2 Slag + 130 54.8% 11.2% 34.0% 4.3%
 15.3% 12.2% 15.0% 205 50  64 77 220 Mix A 30 kg High 1/3/89 Lead Slag
       ie 24%  4 100 kg High 140 54.8% 11.2% 34.0% 4.3% 15.3% 12.2% 14.5%
 360 105 109 62 180 Mix A Lead Slag          ie 29%  2/3/89 5 80 kg High
 200 54.8% 11.2% 34.0% 4.3% 15.3% 12.2% 14.0% 160 160 141 53 280 Mix A
 Lead Slag          ie 100% 3/3/89 6 Continuing + 160 83.1% 16.9% -- --
 20.3% 16.1% 14.2% 105 105 119 68 180 Mix B 30 kg High          ie 100%
 3/3/89 Lead Slag 7 90 kg High 175 83.1% 16.9% -- -- 20.3% 16.1% 13.5%
 115 100   91 55 140 Mix B Lead Slag          ie 87%  4/3/89 8 28 kg
 Reverb 165 82.0% 18.0% -- -- -- 111.7%  22.0% 150 97  92 57 410 Mix B
 Slag +           ie 65%  7/3/89 51 kg Fumes 9 Continuing 170 82.0% 15.0
 -- -- -- 43.9% 19.6%  45 45  50 67 240 Mix B from Run 8          ie 100%
 7/3/89 10 50 kg Slag 120 82.0% 13.0% -- -- -- 24.1% 16.5% 185 145  243
 101  330 Mix B from Run 9 +          ie 78%  8/3/89 12 kg Fume 11 50 kg
 Slag 110 54.6% 12.1% 33.3% 4.0% --  4.4% 13.5% 110 110  180 98 380 Mix A
 from Run 9 +          ie 100% 10/3/89 12 kg Fume 12A Continuing 210
 54.7% 11.8% 33.5% 4.1%  4.3%  3.4% 12.7%  50 50  79 95 300 Mix A from
 Run 11          ie 100% 10/3/89 12B Continuing 300 54.8% 11.2% 34.0%
 4.3% 15.3% 12.2% 12.0% 45 45  60 80 390 Mix A from Run 12A          ie
 100% 10/3/89 13 35 kg Slag 120 82.0% 18.0% -- -- --  1.8% 13.0% 80 80
 202 152  350 Mix B from Run 9 +          ie 100% 13/3/89 8 kg Fume 14
 Continuing 100 82.4% 17.6% -- --  8.4%  6.7% 13.0% 45 32  72 135  185
 Mix B from Run 13          ie 71%  13/3/89 15 40 kg Slag 130 54.6% 12.1%
 33.3% 4.0% --  3.1% 13.0% 95 95 251 159  400 Mix A from Run 9 +
 ie 100% 14/3/89 4 kg Fume 16A Continuing 130 54.7% 11.7% 33.6% 4.2% 6.6%
  5.3% 13.0% 60 57 132 139  295 Mix A from Run 15 14/3/89 16B Continuing
 295 54.8% 11.2% 34.0% 4.3% 15.3% 12.2% 13.0% 35 35  70 120 350 Mix A
 from Run 16A          ie 100% 14/3/89 17 Continuing 185 82.4% 17.6% --
 --  8.5%  6.8% 13.0% 120 90 204 136 495 Mix B from Run 16B          ie
 75%
   14/3/89
 PRODUCTS STEADY STATE STEADY STATE  Bag LANCE AIR RATE OIL RATE  FUME
 RATE  Tapped House Oxygen Rate Excess  g/kg New SMELTING Dry % of New
 Material  RUN Slag Fume Content Nm.sup.3 Oxygen kg/hr Material TEMP  By
 Mass  NUMBER (kg) (kg) (vol %) kg Feed) Content (Total) (See Note)
 (°C.) Measured Balance COMMENTS
   1 68 46 21 2.74 1.1%  9.3 39 1170 to 15% -- Steady operation. Mix A
     1200 27/2/89 2 213 55 21 2.64 1.2%  7.2 16 1200 to 22% -- Steady
 operation. Oil consumption Mix A        1210   dropping as furnace heats
 up. 27/2/89 3 75 + 41 21 4.08 0.9% 14.4 115  1160 to 64% -- Irregular
 operation as plant air low, Mix A 82 in       1180   =) Several stoppages
  to heat bath. 1/3/89 offtake 4 46 + 80 21 4.31 1.7 12.0 103  1180 to
 73% -- Irregular operation as plant air low, Mix A 54 in       1200   =)
 Several stoppages to heat bath. 2/3/89 5 113 100  21 4.67 1.0% 12.3 127
 1220 to 71% -- Reasonably steady operation. Mix A        1240   Rates
 low as plant air still low. 3/3/89 6 60% + 62 21 4.67 2.2% 13.5 116
 1170 to 52% -- Plant air low. Thick slag on furnace Mix B 100 mm
 1250   bottom covering cermet. =) large 3/3/89 sludge          temperatur
 e and oil fluctuations 7 52 + 48 21 5.53 2.1% 15.6 183  1150 to 53% --
 Plant air low. Mix B wall       1180   Accretion buildup on walls.
 4/3/89 accretion 8 110 53 21 4.47 1.5% 19.8 250  1160 to 58% -- Plant
 air low, =) irregular operation Mix B        1190   to start but
 improving towards end of 7/3/89           run 9 148 14 21 3.68 3.2% 16.5
 164  1190 to 28% 44%   Steady operation. Mix B        1210 7/3/89 10 110
 53 21 2.40 3.0% 15.9 102  1140 to 22% 23%   Lance change from 30 mm to
 40 mm at Mix B        1180   start of run due to high lance back- 8/3/89
           pressures. Steady operation after            first 40 kg feed.
 11 74 54 21 2.52 3.0% 13.2 77 1170 to 30% 3.4% Steady operation. Mix A
      1200   Good hygiene. 10/3/89 12A 145 kg  9 21 2.35 3.0%  8.7 33
 1188 to 11% 2.8% Steady operation. Mix A total       1200   Good
 hygiene. 10/3/89 for          Approximately 50 mm stable foam. 12B 12A &amp;
  7 21 3.96 3.0% 11.1 63 1185 to 12% 10.0%  Fairly steady operation.
 Hygiene Mix A 12B       1200   deterioration at this higher coke rate.
 10/3/89           Approximately 100 mm stable foam. 13 138  6 35 0.82
 3.0% 13.2 63 1180 to  5% 8.3% Burner Out Overnight, Bags Oiled =) Mix B
       1210   Re-Bagged Oxygen problems at start. 13/3/89           bath
 held approx 1 hr.            Steady operations once started.
 Good hygiene. 14 76  9 35 0.93 3.0%  6.0 16 1170 to 12% 7.2% Downtime to
 repair oxygen line and Mix B        1220   heat bath. Lost oxygen
 pressure at 13/3/89           end of run. Good hygiene. 15 147  5 35
 0.98% 3.0% 12.0 52 1150 to  2% 3.2% Steady operation. Mix A        1180
  Good hygiene. 14/3/89 16A 105 kg  3 35 1.08 3.0%  6.0 16 1150 to  2%
 5.5% Steady operation apart from 3 min Mix A total       1180   downtime
 to change oxygen bottles. 14/3/89 for          Good hygiene. 16B 16A &amp;
 1 35 1.33 3.0%  2.1 -14  1160 to  2% 12.6%  Steady operation. Mix A 16B
      1180   Approximately 100 mm stable foam. 14/3/89 17 200  9 35 1.00
 3.0%  7.2 25 1170 to  5% 8.4% Initial hygiene problems. Mix B
 1210   25 min downtime for lance change - 14/3/89           burnt
 *Recycle lead sinter plant dust.
 **Lead containing dust from copper coverter electrostatic precipitator.
 Note.
 Specific Cil Rate, Corrected for Furnace Heat Losses.
 (equivalent to 5.6 kg oil/hr for air)
 (equivalent to 3.8 kg oil/hr at 35:02)
 
    
     
                                           TABLE 3
__________________________________________________________________________
             2
ASSAYS (wt %)
RUN
NUM-           Ag  Au
BER         Pb (ppm)
                   (ppm)
                       Zn Fe Cu S   SiO2
                                       Al2O3
                                           CaO
                                              MgO
                                                 As Sb Cd  Bi
__________________________________________________________________________
1    Starting Bath
            42.1
                857
                   --  8.2
                          21.9
                             0.85
                                &lt;0.01
                                    9.2
                                       2.1 1.3
                                              0.86
                                                 0.04
                                                    0.21
                                                       0.004
                                                           &lt;0.001
Mix A
     Final Slag
            8.6
               1700
                   27.7
                       7.5
                          30.3
                             3.19
                                0.25
                                    21.2
                                       3.2 6.5
                                              1.16
                                                 0.23
                                                    0.94
                                                       0.001
                                                           0.003
27/2/89
     Final Fume
            61.4
               2650
                   1.5 7.70
                          0.47
                             0.10
                                5.40
                                    0.60
                                       0.12
                                           0.12
                                              0.12
                                                 2.68
                                                    0.52
                                                       1.090
                                                           0.510
2    Starting Bath
            8.6
               1700
                   27.7
                       7.5
                          30.3
                             3.19
                                0.25
                                    21.2
                                       3.2 6.5
                                              1.16
                                                 0.23
                                                    0.94
                                                       0.001
                                                           0.003
Mix A
     Final Slag
            8.1
               1620
                   20.3
                       6.8
                          29.2
                             3.01
                                0.44
                                    21.9
                                       3.1 7.3
                                              0.95
                                                 0.23
                                                    1.02
                                                       0.002
                                                           0.002
27/2/89
     Final Fume
            59.2
               2024
                   2.3 6.60
                          1.94
                             0.24
                                5.00
                                    1.80
                                       0.29
                                           0.43
                                              0.27
                                                 2.56
                                                    0.40
                                                       1.140
                                                           0.470
3    Starting Bath
            13.0
               1060
                   20.7
                       6.9
                          27.7
                             3.22
                                0.02
                                    19.8
                                       3.0 6.0
                                              1.59
                                                 0.06
                                                    0.85
                                                       0.001
                                                           0.002
Mix A
     Final Slag
            16.6
               1140
                   17.8
                       7.4
                          25.4
                             2.96
                                0.37
                                    19.3
                                       2.8 5.8
                                              1.36
                                                 0.22
                                                    0.87
                                                       0.022
                                                           0.037
1/3/89
     Final Fume
            57.6
               6400
                   17.7
                       6.10
                          1.29
                             0.27
                                5.40
                                    1.90
                                       0.22
                                           0.28
                                              0.21
                                                 3.69
                                                    0.52
                                                       1.460
                                                           0.600
4    Starting Bath
            29.3
                640
                   4.6 8.3
                          25.9
                             1.66
                                &lt;0.01
                                    13.4
                                       2.5 2.8
                                              1.26
                                                 0.03
                                                    0.47
                                                       &lt;0.001
                                                           0.001
Mix A
     Final Slag
            19.2
                660
                   6.3 8.7
                          25.7
                             2.39
                                &lt;0.01
                                    18.6
                                       2.7 4.7
                                              1.34
                                                 0.10
                                                    0.77
                                                       0.008
                                                           0.023
2/3/89
     Final Fume
            59.9
               4437
                   26.5
                       5.80
                          0.76
                             0.19
                                5.80
                                    0.10
                                       0.13
                                           0.12
                                              0.12
                                                 3.12
                                                    0.49
                                                       1.340
                                                           0.470
5    Starting Bath
            27.2
                535
                   1.4 7.7
                          25.1
                             1.75
                                &lt;0.01
                                    15.3
                                       2.6 3.3
                                              1.72
                                                 0.01
                                                    0.49
                                                       &lt;0.001
                                                           0.001
Mix A
     Final Slag
            14.6
                445
                   4.8 7.7
                          26.3
                             2.92
                                &lt;0.01
                                    20.3
                                       3.0 5.9
                                              1.77
                                                 0.11
                                                    0.92
                                                       0.001
                                                           0.001
3/3/89
     Final Fume
            61.0
               4582
                   20.9
                       6.60
                          0.30
                             0.19
                                5.30
                                    -- 0.11
                                           0.08
                                              0.07
                                                 3.64
                                                    0.39
                                                       1.250
                                                           0.520
6    Starting Bath
            36.1
                885
                   2.0 8.1
                          24.2
                             1.25
                                &lt;0.01
                                    10.9
                                       2.3 2.1
                                              0.99
                                                 0.06
                                                    0.36
                                                       0.004
                                                           0.003
Mix B
     Final Slag
            15.1
                220
                   6.1 10.1
                          24.8
                             2.59
                                0.02
                                    18.1
                                       3.4 7.7
                                              1.51
                                                 0.21
                                                    1.04
                                                       0.005
                                                           0.015
3/3/89
     Final Fume
            62.4
               3227
                   19.9
                       3.60
                          0.12
                             0.14
                                6.00
                                    -- 0.10
                                           0.04
                                              0.06
                                                 3.81
                                                    0.36
                                                       1.380
                                                           1.100
7    Starting Bath
            39.4
                770
                   1.5 8.6
                          23.4
                             1.10
                                0.04
                                    9.3
                                       2.2 1.6
                                              0.81
                                                 0.06
                                                    0.30
                                                       &lt;0.001
                                                           0.002
Mix B
     Final Slag
            28.4
                550
                   5.7 9.8
                          20.5
                             2.59
                                &lt;0.01
                                    14.0
                                       2.7 5.3
                                              1.12
                                                 0.28
                                                    0.88
                                                       0.010
                                                           0.076
4/3/89
     Final Fume
            66.1
               3226
                   28.2
                       1.87
                          0.05
                             0.12
                                5.60
                                    -- 0.07
                                           0.03
                                              0.03
                                                 3.82
                                                    0.31
                                                       1.310
                                                           1.050
8    Starting Bath
            27.2
                700
                   3.2 6.2
                          23.1
                             0.79
                                &lt;0.01
                                    15.8
                                       2.9 3.3
                                              1.46
                                                 0.21
                                                    0.36
                                                       0.008
                                                           0.014
Mix B
     Final Slag
            39.2
               1575
                   13.6
                       8.2
                          17.1
                             1.39
                                &lt;0.01
                                    11.0
                                       1.8 3.7
                                              1.06
                                                 0.91
                                                    0.66
                                                       0.152
                                                           0.200
7/3/89
     Final Fume
            60.9
               4880
                   29.2
                       1.34
                          0.07
                             0.11
                                5.30
                                    -- 0.31
                                           0.04
                                              0.04
                                                 2.78
                                                    0.25
                                                       3.600
                                                           0.460
9    Starting Bath
            39.2
               1575
                   13.6
                       8.2
                          17.1
                             1.39
                                &lt;0.01
                                    11.0
                                       1.8 3.7
                                              1.06
                                                 0.91
                                                    0.66
                                                       0.152
                                                           0.200
Mix B
     Final Slag
            39.8
               1435
                   15.6
                       8.2
                          15.5
                             1.71
                                &lt;0.01
                                    10.7
                                       1.8 4.4
                                              0.91
                                                 1.04
                                                    0.78
                                                       0.098
                                                           0.260
7/3/89
     Final Fume
            61.4
               4262
                   28.4
                       1.23
                          0.10
                             0.11
                                5.70
                                    -- 0.11
                                           0.04
                                              0.06
                                                 3.63
                                                    0.25
                                                       3.510
                                                           0.710
10   Starting Bath
            35.3
               1240
                   9.7 8.4
                          30.5
                             1.74
                                &lt;0.01
                                    11.4
                                       2.1 4.1
                                              1.53
                                                 0.42
                                                    0.72
                                                       0.015
                                                           0.102
Mix B
     Final Slag
            40.8
               1065
                   12.8
                       8.9
                          12.5
                             2.84
                                &lt;0.01
                                    11.3
                                       2.0 6.6
                                              0.82
                                                 0.84
                                                    1.14
                                                       0.011
                                                           0.076
8/3/89
     Final Fume
            62.0
               3635
                   23.5
                       1.25
                          0.02
                             0.08
                                5.80
                                    -- 0.08
                                           0.02
                                              0.08
                                                 3.89
                                                    0.21
                                                       2.570
                                                           1.710
11   Starting Bath
            42.2
               1100
                   9.8 8.3
                          17.0
                             1.41
                                &lt;0.01
                                    10.2
                                       1.8 3.9
                                              0.92
                                                 0.70
                                                    0.65
                                                       0.020
                                                           0.102
Mix A
     Final Slag
            41.4
               2016
                   13.6
                       8.2
                          15.7
                             2.05
                                0.01
                                    11.1
                                       1.5 4.1
                                              0.56
                                                 1.10
                                                    0.86
                                                       0.060
                                                           0.126
10/3/89
     Final Fume
            59.6
               7042
                   12.1
                       0.79
                          0.03
                             0.09
                                4.60
                                    -- 0.10
                                           0.02
                                              0.02
                                                 5.50
                                                    0.31
                                                       3.210
                                                           0.880
12A  Starting Bath
            41.4
               2016
                   13.6
                       8.2
                          15.7
                             2.05
                                0.01
                                    11.1
                                       1.5 4.1
                                              0.56
                                                 1.10
                                                    0.86
                                                       0.060
                                                           0.126
Mix A
     Final Slag
            33.0
               2216
                   17.3
                       8.1
                          16.1
                             2.23
                                0.03
                                    12.2
                                       1.6 4.6
                                              0.53
                                                 1.20
                                                    0.91
                                                       0.127
                                                           0.170
10/3/89
     Final Fume
            60.6
               6269
                   24.7
                       1.33
                          0.16
                             0.15
                                6.00
                                    -- 0.12
                                           0.05
                                              0.07
                                                 3.42
                                                    0.34
                                                       2.940
                                                           0.450
12B  Starting Bath
            38.0
               2216
                   17.3
                       8.1
                          16.1
                             2.23
                                0.03
                                    12.2
                                       1.6 4.6
                                              0.53
                                                 1.20
                                                    0.91
                                                       0.127
                                                           0.170
Mix A
     Final Slag
            37.6
               2192
                   17.4
                       8.1
                          16.1
                             2.15
                                &lt;0.01
                                    11.8
                                       1.6 4.5
                                              0.61
                                                 1.20
                                                    0.89
                                                       0.160
                                                           0.181
10/3/89
     Final Fume
            58.2
               6687
                   25.3
                       0.85
                          0.09
                             0.18
                                6.60
                                    -- 0.11
                                           0.04
                                              0.07
                                                 3.23
                                                    0.35
                                                       2.960
                                                           0.460
13   Starting Bath
            38.0
               1038
                   10.4
                       8.7
                          19.5
                             1.36
                                &lt;0.01
                                    10.4
                                       1.9 3.3
                                              0.86
                                                 0.55
                                                    0.62
                                                       0.021
                                                           0.070
Mix B
     Final Slag
            39.7
               1457
                   24.7
                       8.1
                          12.9
                             2.40
                                0.06
                                    10.8
                                       1.9 6.4
                                              0.60
                                                 1.30
                                                    1.11
                                                       0.193
                                                           0.221
13/3/89
     Final Fume
            57.2
               4514
                   25.8
                       1.09
                          0.07
                             0.14
                                5.30
                                    -- 0.15
                                           0.05
                                              0.04
                                                 4.14
                                                    0.30
                                                       3.830
                                                           1.220
14   Starting Bath
            39.7
               1457
                   24.7
                       8.1
                          12.9
                             2.40
                                0.06
                                    10.8
                                       1.9 6.4
                                              0.60
                                                 1.30
                                                    1.11
                                                       0.193
                                                           0.221
Mix B
     Final Slag
            34.9
               1405
                   26.2
                       8.9
                          14.4
                             2.78
                                0.01
                                    12.1
                                       2.3 7.6
                                              0.71
                                                 1.34
                                                    1.26
                                                       0.124
                                                           0.231
13/3/89
     Final Fume
            60.3
               3831
                   36.0
                       1.49
                          0.17
                             0.13
                                5.50
                                    -- 0.14
                                           0.06
                                              0.05
                                                 3.63
                                                    0.29
                                                       3.090
                                                           0.850
15   Starting Bath
            26.8
                793
                   11.2
                       9.0
                          22.5
                             2.26
                                &lt;0.01
                                    13.2
                                       2.6 5.9
                                              1.28
                                                 0.47
                                                    0.93
                                                       0.068
                                                           0.109
Mix A
     Final Slag
            30.7
               2016
                   18.1
                       8.2
                          18.1
                             2.65
                                &lt;0.01
                                    14.1
                                       1.9 5.5
                                              0.64
                                                 0.98
                                                    1.07
                                                       0.101
                                                           0.193
14/3/89
     Final Fume
            57.7
               5499
                   41.0
                       2.18
                          0.64
                             0.18
                                4.90
                                    -- 0.09
                                           0.05
                                              0.05
                                                 5.44
                                                    0.35
                                                       2.640
                                                           0.770
16A  Starting Bath
            30.9
               2016
                   18.1
                       8.2
                          18.1
                             2.65
                                &lt;0.01
                                    14.1
                                       1.9 5.5
                                              0.64
                                                 0.98
                                                    1.07
                                                       0.101
                                                           0.193
Mix A
     Final Slag
            30.0
               2038
                   15.3
                       8.4
                          18.9
                             2.80
                                &lt;0.01
                                    14.6
                                       1.9 5.6
                                              0.60
                                                 0.95
                                                    1.08
                                                       0.102
                                                           0.199
14/3/89
     Final Fume
            58.0
               5967
                   41.2
                       2.13
                          0.87
                             0.25
                                4.80
                                    -- 0.15
                                           0.13
                                              0.09
                                                 5.18
                                                    0.41
                                                       2.440
                                                           0.730
16B  Starting Bath
            30.0
               2038
                   15.3
                       8.4
                          18.9
                             2.80
                                &lt;0.01
                                    14.6
                                       1.9 5.6
                                              0.60
                                                 0.95
                                                    1.08
                                                       0.102
                                                           0.199
Mix A
     Final Slag
            30.2
               2030
                   14.9
                       8.2
                          18.0
                             2.66
                                &lt;0.01
                                    15.5
                                       1.9 5.5
                                              0.58
                                                 0.89
                                                    1.06
                                                       0.131
                                                           0.213
14/3/89
     Final Fume
            57.6
               7330
                   27.1
                       1.28
                          0.37
                             0.25
                                4.50
                                    -- 0.09
                                           0.07
                                              0.02
                                                 6.34
                                                    0.49
                                                       2.810
                                                           0.740
17   Starting Bath
            30.2
               2030
                   14.9
                       8.2
                          18.0
                             2.66
                                &lt;0.01
                                    15.5
                                       1.9 5.5
                                              0.58
                                                 0.89
                                                    1.06
                                                       0.131
                                                           0.213
Mix B
     Final Slag
            32.7
               1289
                   17.3
                       9.0
                          15.7
                             2.81
                                &lt;0.01
                                    13.0
                                       2.3 7.2
                                              0.85
                                                 0.90
                                                    1.21
                                                       0.105
                                                           0.260
14/3/89
     Final Fume
            58.0
               4486
                   36.9
                       1.77
                          0.85
                             0.21
                                5.60
                                    -- 0.08
                                           0.06
                                              0,.08
                                                 4.18
                                                    0.35
                                                       2.820
                                                           0.720
Note. Average Steady State Slags
are for Mix A:
            31.1
               2843
                   23.2
                       7.6
                          15.8
                             2.45
                                0.01
                                    11.6
                                       1.7 4.35
                                              0.48
                                                 2.25
                                                    0.93
                                                       0.675
                                                           0.329
Mix B:      40.4
               1603
                   31.6
                       7.1
                          9.1
                             2.57
                                0.01
                                    8.9
                                       1.9 6.03
                                              0.57
                                                 2.27
                                                    1.02
                                                       1.060
                                                           0.393
__________________________________________________________________________
 
    
     EXAMPLE 2 
     Consideration of the 250 kg scale testwork has resulted in the flowsheet for the production plant shown in FIG. 1. 
     This proposed ISASMELT plant will smelt either Mix A or B material, or any combination thereof, and two specific scale up options are considered in this example: 
     Option 1: Smelt 4 tph of by-product lead dusts together with 2 tph of low lead pyritic concentrate, giving a total treatment rate of 3600 tonnes per month at an availability of 80%. 
     Option 2: Smelt only lead dusts at a rate of 4 tph, giving a treatment rate of 2400 tonnes per month at an availability of 80%. 
     A budget estimate for an ISASMELT plant has been developed and is shown in Table 4 and the cost estimate in Tables 5 and 6. 
     
                       TABLE 4
______________________________________
PROCESS SUMMARY
           Option 1    Option 2
______________________________________
Material     MIX A         MIX B
             54.7% recycle 82% recycle
             lead dust     lead dust
             12.0% converter
                           18% converter dust
             dust
             33.3% pyritic
             concentrate
Treatment rate, ie @
             6 tonnes/hr   4 tonnes/hr
80% availability
             3600 tonnes/month
                           2400 tonnes/month
Lead slag product
             5.0 tonnes/hr 3.2 tonnes/hr
             (31% Pb,      (40% Pb,
             &lt;0.05% S)     &lt;0.05% S)
Operating    1170 to 1190° C.
                           1170 to 1190° C.
temperature
Lance air (35% 0.sub.2)
Blower @ 150 kPa
             1.33 Nm.sup.3 /s
                           0.75 Nm.sup.3 /s
Oxygen @ 150 kPa
             0.29 Nm.sup.3 /s
                           0.16 Nm.sup.3 /s
             (36 tpd)      (20 tpd)
Coke breeze  650 kg/hr     510 kg/hr
Natural gas  125 Nm.sup.3 /hr
                           125 Nm.sup.3 /hr
(standby burner)
             10% duty cycle
                           10% duty cycle
Silica flux  240 kg/hr     --
Recycle fume 300 kg/hr     200 kg/hr
(5% of feed)
Spray cooling water
             1.5 liters/s  1.1 liters/s
Furnace offgas
Wet          4.9 Nm.sup.3 /s
                           3.6 Nm.sup.3 /s
Dry          2.6 Nm.sup.3 /s @ 8.4%
                           2.0 Nm.sup.3 /s @ 4.9%
             SO.sub.2      SO.sub.2
Dust loading 10 g/m.sup.3  9 g/m.sup.3
(wet gas @ 200° C.)
Offgas after 2.8 Nm.sup.3 /s @ 7.8%
                           2.2 Nm.sup.3 /s @ 4.5%
process      SO.sub.2      SO.sub.2
gas baghouse (dry basis)   (dry basis)
______________________________________
 
    
     
                       TABLE 5
______________________________________
BUDGET CAPITAL ESTIMATE
FOR ISASMELT PLANT
                     Australian
______________________________________
Mixer                  $  100 000
Feed Conveyor          50 000
ISASMELT vessel (refractory lined,
                       ↓↓↓ ↓↓↓
1.0⊥⊥ ID)
Lance handling         75 000
Plenum                 50 000
Control room           75 000
Process air blower (400 kW)
                       200 000
Process air line       75 000
Process gas fluo (150M)
                       75 000
Structural steel       350 000
Foundations            150 000
SUBTOTAL               $2 000 000
Process gas baghouse   200 000
Process gas fan        40 000
Chain conveyor         75 000
SUBTOTAL               $2 315 000
Instrumentation @ 10%  231 500
Electrics @ 10%        231 500
Engineering design @ 20%
                       463 000
SUBTOTAL               $3 241 000
Contingency @ 30%      972 000
Total budget capital estimate
                       AU$4 213 000
______________________________________
 Exclusions:
 Feed bins and weighers
 Hygiene ventilation requirements
 Product handling, i.e., slag granulation or casting
 Provision of services
 
    
     
                       TABLE 6
______________________________________
PART 1
Operating Cost Estimate for Option 1
Smelting 6 tonnes/hr of Lead Dusts and Concentrate
at 80% availability
______________________________________
                              ANNUAL
                              COST
ITEM      BASIS FOR ESTIMATE  AUD (1000)
______________________________________
Labour    1/2 Metallurgist/Supervisor
                               40
          12 Operators (ie 3 per shift)
                              568
Oxygen    0.29 Nm.sup.3 /s by 80%
                              978
Coke breeze
          650 kg/hr by 80%    170
Flux      240 kg/hr by 80%     12
Natural gas
          125 Nm.sup.3 /hr by 10%
                               19
          (heating and holding)
Engineering
          Labour: 1 Fitter     47
maintenance
          Materials: Based on current
                              100
          ISASMELT usage
Other stores
          Based on current ISASMELT
                              150
          usage
Refractories
          50 tonnes Chrome-Magnesite
                              200
          bricks (1 year life) plus
          Launders, etc. (labour and
          materials
Baghouse bags
          630 m.sup.2 Ryton bags
                               43
          (bag life of 1 year)
Compressed air
          Based on current ISASMELT
                               50
          usage
          (baghouse and general)
Power     Total power usage 500 kW
                              178
Fresh Water
          6 m.sup.3 /hr by 90%
                               5
          (flue spray and general)
Transport Based on material moved
                               82
TOTAL COST                    2640
UNIT COST PER TONNE OF LEAD
33800 tonnes slag produced pa @ 31% Pb
                          AUD252
______________________________________
PART 2
Operating Cost Estimate for Option 2
Smelting 4 tonnes/hr of Lead Dusts at 80% availability
______________________________________
                              ANNUAL
                              COST
ITEM      BASIS FOR ESTIMATE  AUD (1000)
______________________________________
Labour    1/2 Metallurgist/Supervisor
                               40
          12 Operators (ie 3 per shift)
                              568
Oxygen    0.16 Nm.sup.3 /s by 80%
                              540
Coke breeze
          510 kg/hr by 80%    133
Flux      None required        0
Natural gas
          125 Nm.sup.3 /hr by 10%
                               19
          (heating and holding)
Engineering
          Labour: 1 Fitter     47
maintenance
          Materials: Based on current
                              100
          ISASMELT usage
Other stores
          Based on current ISASMELT
                              150
          usage
Refractories
          50 tonnes Chrome-Magnesite
                              200
          bricks (1 year life) plus
          Launders, etc. (labour and
          materials)
Baghouse bags
          630 m.sup.2 Ryton bags
                               32
          (bag life of 1 year)
Compressed air
          Based on current ISASMELT
                               50
          usage
          (baghouse and general)
Power     Total power usage 500 kW @
                              178
          USDO.030/kWH
Fresh Water
          5 m.sup.3 /hr by 90%
                               4
          (flue spray and general)
Transport Based on material moved
                               54
TOTAL COST                    2115
UNIT COST PER TONNE OF LEAD
21700 tonnes slag produced pa @ 40% Pb
                          AUD244
______________________________________
 
    
     The maximum smelting rates used during the 250 kg testwork were 150 to 160 kg/hr for Mix A and B materials, indicating that a furnace of 1.3 m internal diameter would smelt in excess of 6 tonnes/hr. For greater operating flexibility, however, a diameter of 1.8 m is preferred for both Options 1 and 2. 
     The lance air rates used during the 250 kg testwork are calculated to give a slight oxygen excess, possibly 3%, in the offgas in addition to fully oxidizing the feed and burning the coke and oil. An excess oxygen concentration has been shown from the Applicant&#39;s plant operating experience to provide optimum smelting conditions. 
     The smelting air rates enriched to 35% O 2  used during the trials were 0.421 Nm 3  /kg of Mix A and 0.175 Nm 3  /kg of Mix B, with a fuel combustion air rate of 5.09 Nm 3  /kg of coke breeze. Scaling in proportion, the lance air requirement enriched to 35% O 2  on a production plant is 1.62 Nm 3  /s for Option 1 and 0.91 Nm 3  /s for Option 2. 
     The air component of these flowrates is 1.33 Nm 3  /s for Option 1 and 0.75 Nm 3  /s for Option 2. The air supply pressure is 150 kPa for low pressure lances, supplied from a single stage blower. 
     The oxygen consumptions to enrich the lance air to 35% O 2  are 36 and 20 tonnes per day for Options 1 and 2 respectively. Oxygen enrichment is used to increase the SO 2  concentration in the process offgas to aid SO 2   recovery in an acid plant and to reduce the offgas volumes. 
     During the 250 kg testwork, both coke breeze and oil were used together as fuels in varying proportions. In the final runs at 35% O 2 , coke breeze additions up to 10 times the oil rate were used. Under these conditions, the furnace was over-coked and a stable foam approximately 100 mm thick formed on the bath surface. The foam did not cause problems and is not present when the furnace is correctly coked. The use of coke breeze as the sole fuel is preferred. 
     The fuel consumptions in coke equivalents during the trials at 35% O 2  were 90 kg coke breeze/dry tonne of Mix A and 100 kg coke breeze/dry tonne of Mix B, at 5% fume recycle and 15% moisture in the feed, after correcting for heat losses from the 250 kg rig. The furnace heat losses on the proposed plant are estimated to be a maximum of 0.5 MW which is equivalent to 110 kg of coke breeze per hour at 35% O 2 . 
     The resultant fuel consumptions are 650 kg coke breeze/hr for Option 1 and 5l0 kg coke breeze/hr for Option 2. 
     The process gas at the top of the furnace, including 1 Nm 3  /s ingress air, is shown in Table 7 below: 
     
                       TABLE 7
______________________________________
         Option 1    Option 2
         6 tonnes/hr Mix A
                     4 tonnes/hr Mix B
______________________________________
O.sub.2    9.4%          11.7%
N.sub.2    69.8%         70.3%
SO.sub.2   8.4%          4.9%
CO.sub.2   12.4%         13.1%
TOTAL      2.6 Nm.sup.3 /s
                         2.0 Nm.sup.3 /s
           (dry basis)   (dry basis)
______________________________________
 
    
     The spray water required to cool the gas to 200° C. is 1.5 liters/s for Option 1 and 1.1 liters/s for Option 2, giving total wet offgas volumes of 4.9 and 3.6 Nm 3  /s respectively. 
     A dedicated process gas baghouse with integral fume return system enables the fume to be recycled directly to the ISASMELT furnace at the same rate as it is produced. This stabilises the process by automatically correcting any excursions and thus improves metallurgical control. This is especially preferred for the lower lead slags of Option 1. 
     Pulse air plus ingress for a reverse pulse baghouse is estimated to be 0.2 Nm 3  /s for both Options 1 and 2. The gas volumes and SO 2  concentrations entering the acid plants will thus be 2.8 Nm 3  /s at 7.8% SO 2  and 2.2 Nm 3  /s at 4.5% SO 2  (both on a dry basis) for Options 1 and 2 respectively. 
     The fume rates during the 250 kg testwork were dependent upon the gas volume flushed through the bath. For lance air enriched to 35% O 2  the fume rate ranged from 5 to 10% by weight or the reed. Fuming tended to be slightly greater for Mix B material, in accordance with the higher PbO activity in the slag, but this difference was not significant at 35% O 2 . On a full size plant the fume rate will be approximately 5% of the feed rate. 
     During the 250 kg testwork it was not possible to recycle the fume from the baghouse directly on the plant, instead the fume from previous runs was pelletized and added at the same rate as that measured at the baghouse. 
     As a result, the minor elements in the fume did not reach steady state except for antimony (Table 3). The steady state fume compositions are estimated as 0.4% Sb, 10% As, 1.5% Bi and 15% Cd for Mix A and 0.4% Sb, 10% As, 1.5% Bi and 20% Cd for Mix B. 
     Silver and gold in the fume did not reach steady state during the testwork. The steady state fume compositions are estimated as 8000 ppm Ag and 40 ppm Au for Mix A, and 5000 ppm Ag and 50 ppm Au for Mix B. Silver and gold were fully recovered once the fume was recycled. 
     The furnace may be either batch or continuously tapped, although due to the relatively low tonnages batch tapping is preferred to maintain reasonable slag flowrates and to minimize labour. 
     The holding capacity of a 1.8 m internal diameter furnace will allow 2.5 hours operation between taps for Option 1 and 4 hours for Option 2. 
     The slag may be either granulated or cast depending upon requirements. 
     Lance lives currently average 100 hour operating times. 
     The furnace is lined with chrome-magnesite wear bricks and based on current refractory lives a minimum period of one year is expected between rebricks. 
     Since the ISASMELT furnace is almost totally enclosed and a moist agglomerate feedstock is used good hygiene is likely to be achieved. 
     Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.