as illustrated in fig1 solvent and a solution containing an extractable metal ion or other material are mixed in a dispersion producing means identified as the dispenser 10 . the mixing apparatus , dispenser 10 , can be an agitated or sonic mixing device or any of several motionless mixing devices or flow restricting devices such as orifices , valves , or baffles . in a preferred embodiment , the mixing apparatus is the motionless mixing device described n armeniades et al , u . s . pat . no . 3 , 286 , 992 , and illustrated in fig2 and 3 . as shown in fig2 and 3 , the device 10 is in the form of a hollow conduit 11 of cylindrical crosssection containing a plurality of curved , sheet - like elements 12 . each of the elements 12 is a flat sheet which is twisted so that the upstream and downstream edges of each element 12 are at a substantial angle to each other . this angle may vary from about 60 ° to about 210 °. the twist of the elements shown in fig2 and 3 is about 180 °. also , each successive element 12 is twisted so the upstream edge of one element will be at a substantial angle from the downstream edge of the preceding element . a 90 ° angle of orientation is shown in fig2 and 3 . finally , the twist of each successive element may be reversed from the twist of the element preceding it . that is , the elements may be arranged in alternating left - handed and right - handed curvature groups , or alternatively , a series of left - handed elements could be followed by a series of right - handed elements . the elements are preferably the width of the inner diameter conduit and have a length of up to several times their width . the elements may be separate entities although it is desired that they be physically connected to maintain proper orientation for optimum mixing . by controlling the above factors , as well as the number of elements and velocity of the fluid through the motionless mixer , a dispenser 10 can be designed which will produce an optimum drop size of solute in solvent for mass transfer to occur . referring back now to fig1 the dispersed fluids are then conveyed to a residence chamber 14 which is designed to permit sufficient contacting time for mass transfer of the metal ion or other material to occur from the solute to the solvent phase , and preferably for the system to reach equilibrium . the residence chamber 14 may comprise a vertically oriented container or length of pipe , or in certain cases where the two phases are so dispersed that little if any separation will occur , the residence chamber can be of any convenient configuration which will promote and prolong contact between the dispersed phases . for most solvent extraction operations where the solvent phase is an organic liquid less dense than the solute phase , the residence chamber 14 will be a vertical chamber with flow designed to go downwardly through the chamber . in this manner , the downward flow of the continuous solvent phase will closely match the tendency of the heavier solute phase to migrate downwardly and any substantial separation of the phases will be prevented . specific parameters for the residence chamber such as chamber size and flow rate through the chamber will depend on the particular solvent and solute in the system . it has been found that a residence chamber - to - mixer cross - sectional area ratio of at least 4 to 1 will ensure no significant separation of the dispersed phases and yet permit sufficient contact time for mass transfer between the phases to occur . as shown in fig1 after the dispersed phases have passed through the residence chamber 14 , they are then redispersed in a drop size conditioner 15 to establish a mean drop size in the discontinuous phase which will enable easier separation of the phases . the drop size conditioner also serves the purpose of reducing entrainment of the continuous phase liquid in the discontinuous phase liquid . preferably , the drop conditioner is a hollow conduit containing mixing elements as illustrated in fig2 and 3 . such a design will produce a narrow range distribution of drop sizes which facilitate separation in the settler . however , the design parameters of the drop size conditioner may be quite different from the disperser in the mixing stage of the process . for example , in those solvent extraction systems in which quite small drop sizes are required for the desired amount of mass transfer to take place in the mixing stage , the result may be an emulsion or stable , noncoalescing dispersion which is difficult to separate . the mixing action of the drop size conditioner 15 can then be designed to cause contacting and coalescence of the very small drops and produce a new , larger mean drop size distribution in the dispersion which is more easily separated in the settling stage . moreover , the mixing action of the drop size conditioner has been found to reduce entrainment of the continuous phase in the discontinuous phase due to coalescence of entrained liquid through increased contact with the continuous liquid phase . finally , as illustrated in fig1 the conditioned dispersion from the conditioner 15 enters a settling chamber 16 which may be either a gravitational or centrifugal settler . for most solvent extraction operations , gravitational separation in a horizontal pipe settler has been found to produce good results . additionally , the inclusion of bafflers in the settler has been found to reduce entrainment of organic liquid in the aqueous liquid phase and the entrainment of water in the organic phase . the solvent extraction apparatus of the present invention can also be set up to recycle the solute phase as illustrated in fig4 . in this manner , improved stripping of metal ions from the solute phase to the solvent phase is achieved . this is because the recycle of the major portion of the solute stream results in a multi - pass operation where the effective solvent to solute ratio is greatly increased . as illustrated in fig4 solute containing strippable metal ions is pumped from a reservoir 20 , through a filter 21 , a metering valve 22 , and a flow meter 23 into the mixing section , consisting of the disperser 10 and chamber 14 . the solution may optionally be maintained under pressure fron an inert gas source 25 to prevent oxidation . at the same time solvent is pumped from a second reservoir 24 by a pump 26 through a metering valve 27 and flow meter 28 into the inlet of mixing section . there , both streams are mixed with a recycle stream containing the major portion of solute passing through the system in the separating stage consisting preferably of the conditioner 15 and settler 16 , solvent is collected in tank 30 and may then be sent to a metal recovery operation prior to its own recycle back to reservoir 24 . solute is pumped through line 32 via pump 34 back to the mixing section of the system . only a small portion of the solute phase is removed from the system via line 36 to a collection tank 38 . in this manner , the system can be operating at a 0 . 5 to 1 or 1 to 1 solvent to solute ratio in the mixing stage of the system , and yet the overall system will be operating on an overall solvent to solute ratio on the order of 10 / 1 to 100 / 1 . use of such a high overall solvent to solute ratio enables attainment of equilibrium operation while using a short residence time mixing stage . the process of the present invention is illustrated by the following examples which are in no way to be construed as limitative of the invention . a series of liquid extractions were carried out on uranium - containing aqueous phosphoric acid streams . the organic liquid extraction agent was a kermac 470b solution , a mixture of hydrocarbons containing approximately 34 % paraffins , 49 % naphthenes , and 17 % aromatics available from kerr - mcgee corp . containing 0 . 5 diethylhexyl phosphoric acid and 0 . 125 m tri - n - octylphosphine oxide . the following general test parameters were utilized : ______________________________________flow velocities 1 . 3 - 2 . 3 feet per secondcontinuous phase organic ( o / a ratios of 0 . 5 / 1 to 2 . 7 / 1 ) mixer diameter 0 . 602 inches i . d . number of mixer elements 12 to 72residence chambers 3 inch i . d ., horizontal and verticalresidence times 1 to 9 secondssettling time 10 minutes______________________________________ all measurements of uranium concentrations in both the organic and aqueous process streams were made using the colorado school of mines colorimetric technique which utilizes tributyl phosphate in isooctane to extract uranyl ions from an aluminum nitrate solution . color is developed by introducing an aliquot of the extract into an acetone - water solution of dibenzoyl - methane and pyridine . the lower limit for uranium analysis using this method is 25 ppm . all entrainment measurements of organic in the aqueous phase were made using a perkin elmer model 137g infrared spectrophotometer . this method of measurement is accurate to within t 5 ppm . the results of the tests are reported in table i as follows : table i______________________________________ ve - resi - no . of loc - dence organic / test mixing ity residence time aqueous temp . no . elements ( fps ) chambers ( sec ) ratio (° c . ) ______________________________________1 24 2 . 2 none 1 . 4 2 . 7 / 1 422 72 2 . 2 &# 34 ; 4 . 1 2 . 3 / 1 333 72 1 . 9 &# 34 ; 4 . 7 2 . 6 / 1 364 72 1 . 8 &# 34 ; 4 . 8 1 . 8 / 1 405 72 2 . 1 &# 34 ; 4 . 4 2 . 6 / 1 396 72 1 . 9 &# 34 ; 4 . 7 2 . 6 / 1 327 12 1 . 9 3 &# 34 ; hor . 8 . 1 2 . 2 / 1 418 12 2 . 0 3 &# 34 ; hor . 7 . 4 2 . 3 / 1 459 12 1 . 9 3 &# 34 ; vert . 7 . 5 2 . 5 / 1 4210 12 1 . 6 3 &# 34 ; vert . 7 . 5 2 . 6 / 1 4011 12 2 . 1 3 &# 34 ; vert . 7 . 0 0 . 6 / 1 4512 12 2 . 0 3 &# 34 ; vert . 7 . 8 2 . 3 / 1 4513 12 1 . 9 3 &# 34 ; hor . 8 . 0 2 . 4 / 1 4414 12 1 . 9 3 &# 34 ; hor . 8 . 0 2 . 5 / 1 45______________________________________ ura - entrain - nium uranium uranium uranium % ment org . in aq . from org . after ex - test in aq . feed mixer - aq . feed mixer trac - no . ( ppm ) ( ppm ) ( ppm ) ( ppm ) ( ppm ) tion______________________________________1 55 180 55 0 62 692 102 177 25 0 75 863 127 177 30 0 68 834 290 195 60 0 90 685 120 195 40 0 83 816 82 190 35 0 63 817 90 191 40 26 95 798 72 191 37 31 95 809 75 220 83 31 101 6110 45 217 81 30 91 6111 127 210 131 37 180 3512 82 210 43 33 116 8013 67 183 67 25 101 6314 35 152 55 37 77 63______________________________________ table i - a______________________________________ ve - resi - no . of loc - dence organic / test mixing ity residence time aqueous temp . no . elements ( fps ) chambers ( sec ) ratio (° c . ) ______________________________________15 72 2 . 0 none 4 . 6 2 . 4 / 1 5016 72 2 . 0 &# 34 ; 4 . 4 2 . 4 / 1 4417 72 2 . 0 &# 34 ; 4 . 6 2 . 6 / 1 3918 72 1 . 9 &# 34 ; 4 . 7 2 . 4 / 1 3819 72 1 . 9 &# 34 ; 4 . 7 2 . 2 / 1 2120 72 2 . 2 &# 34 ; 4 . 1 0 . 56 / 1 4321 12 1 . 8 &# 34 ; 1 . 4 2 . 2 / 1 4122 12 1 . 9 &# 34 ; 1 . 6 2 . 6 / 1 4123 12 1 . 3 &# 34 ; 2 . 3 2 . 1 / 1 4124 12 1 . 8 3 &# 34 ; hor . 8 . 5 2 . 4 / 1 4125 12 2 . 0 3 &# 34 ; vert . 7 . 6 2 . 3 / 1 43______________________________________entrain - ura - ment nium uranium uranium uranium % org . in aq . from org . after ex - test in aq . feed mixer - aq . feed mixer trac - no . ( ppm ) ( ppm ) ( ppm ) ( ppm ) ( ppm ) tion______________________________________15 290 180 75 40 82 5816 97 180 61 40 97 6717 140 180 61 40 103 6718 100 150 40 35 62 7319 80 186 46 38 121 7520 300 186 100 38 198 4621 60 186 66 30 93 6422 40 186 72 30 82 5823 20 172 95 30 94 4524 37 172 70 30 95 5925 50 172 74 30 95 59______________________________________ as can be seen , the extraction efficiencies achieved using only 12 mixing elements in combination with a residence chamber compare favorably to a more expensive mixer having 72 mixing elements and no residence chamber , over a range of organic phase to aqueous phase ratios . again , a series of liquid extractions were carried out on uranium containing aqueous phosphoric acid streams . the organic liquid extraction agent was the same as in example i . the apparatus was arranged as illustrated in fig5 . the following general test parameters were utilized : ______________________________________flow velocities 1 . 8 - 2 . 4 feet per secondcontinuous phase organicmixer diameter 0 . 25 inch i . d . number of mixer elements 48residence chamber ( where 1 inch i . d ., 14 inchesindicated ) long ( vertical ) residence times 1 . 5 to 12 secondssettling time 10 minutes______________________________________ the results of the tests are reported in table ii as follows : table ii______________________________________ entrain - ve - resi - mentloc - dence organic / org . test ity residence time aqueous temp . in aq . no . ( fps ) chamber ( sec ) ratio (° c .) ( ppm ) ______________________________________26 1 . 8 no 1 . 6 2 . 4 / 1 38 4027 2 . 0 &# 34 ; 1 . 5 2 . 0 / 1 38 8728 2 . 2 &# 34 ; 1 . 4 2 . 0 / 1 39 4829 2 . 2 &# 34 ; 1 . 4 2 . 5 / 1 37 4030 2 . 1 &# 34 ; 1 . 4 2 . 5 / 1 36 3531 2 . 0 &# 34 ; 1 . 5 0 . 28 / 1 37 11532 2 . 3 &# 34 ; 1 . 3 2 . 65 / 1 35 3333 2 . 4 &# 34 ; 1 . 2 2 . 45 / 1 39 5834 2 . 0 &# 34 ; 1 . 5 2 . 23 / 1 39 7735 2 . 0 &# 34 ; 1 . 5 2 . 2 / 1 37 6036 2 . 0 &# 34 ; 1 . 5 2 . 4 / 1 36 6537 2 . 1 &# 34 ; 1 . 4 2 . 5 / 1 37 -- 38 2 . 2 &# 34 ; 1 . 4 2 . 9 / 1 33 -- 39 2 . 1 &# 34 ; 1 . 4 1 . 8 / 1 37 -- ______________________________________ % uranium uranium uranium uranium in ex - test in feed from mixer org . feed org . from trac - no . ( ppm ) ( ppm ) ( ppm ) mixer ( ppm ) tion______________________________________26 165 102 148 185 3827 165 86 154 205 4828 165 85 154 213 4829 166 65 63 123 6130 166 61 66 119 6331 166 111 63 316 3332 165 48 0 57 7133 165 35 0 61 7834 165 101 141 186 3935 166 97 144 187 4136 85 74 61 69 1337 90 49 170 201 4638 83 34 170 202 5839 83 50 182 190 48______________________________________ table ii - a______________________________________ entrain - ve - resi - mentloc - dence organic / org . test ity residence time aqueous temp . in aq . no . ( fps ) chamber ( sec ) ratio (° c .) ( ppm ) ______________________________________40 2 . 2 no 1 . 4 3 . 0 / 1 36 6541 2 . 0 &# 34 ; 1 . 5 2 . 8 / 1 34 -- 42 2 . 4 &# 34 ; 1 . 2 2 . 6 / 1 39 6043 2 . 0 &# 34 ; 1 . 5 2 . 2 / 1 39 5044 2 . 2 &# 34 ; 1 . 4 1 . 5 / 1 40 14045 2 . 3 &# 34 ; 1 . 3 1 . 1 / 1 37 8746 2 . 2 yes 1 . 2 2 . 7 / 1 33 -- 47 2 . 1 &# 34 ; 1 . 2 2 . 2 / 1 37 -- 48 2 . 3 &# 34 ; 1 . 2 0 . 36 / 1 35 -- 49 2 . 2 &# 34 ; 1 . 2 0 . 64 / 1 42 11250 2 . 1 &# 34 ; 1 . 2 0 . 5 / 1 39 7551 2 . 0 yes 1 . 2 2 . 5 / 1 34 5752 2 . 1 yes 1 . 2 2 . 3 / 1 35 -- 53 1 . 9 no 1 . 5 0 . 57 / 1 39 -- 54 2 . 2 no 1 . 4 2 . 6 / 1 36 -- ______________________________________ % uranium uranium uranium uranium in ex - test in feed from mixer org . feed org . from trac - no . ( ppm ) ( ppm ) ( ppm ) mixer ( ppm ) tion______________________________________40 158 113 223 246 2841 158 106 233 247 3342 165 99 235 257 4043 165 100 235 254 3944 167 110 237 288 3545 167 91 235 320 4546 169 81 243 276 5247 169 90 243 297 4748 169 114 243 421 3349 167 105 153 281 3850 167 98 153 309 4151 167 71 153 201 5852 165 72 151 202 5753 165 112 151 276 3254 165 85 151 195 48______________________________________ as shown in table ii , the extraction efficiency is dependent on the concentration of uranium in the respective aqeuous and organic feed streams . the higher the concentration of uranium in the organic feed stream , the lower the extraction efficiency . however , direct comparison of runs having substantially the same uranium concentrations in both the aqueous and organic feed streams shows that using the same number of mixing elements , the apparatus with a residence chamber has a 9 - 12 % greater extraction efficiency than the apparatus without a residence chamber . this can be seen by comparing runs 46 and 52 ( with residence chamber ) with runs 42 and 54 ( without residence chamber ), respectively . a test was made to determine the effect of the drop size conditioning elements of the apparatus on entrainment of organic in the aqeuous phase of a process stream . the organic phase was kermac 470b and lix 64 , a hydroxy oxime compound , available from general mills . the aqueous phase was ranchers electrolyte , a loaded 5 n h 2 so 4 solution available from ranchers , inc . containing approximately 40 gm / l of copper . the apparatus was set up as illustrated in fig6 with the solvent and solute being pumped through a 6 element drop conditioner 15 , a first residence chamber 14 , a second 6 element drop conditioner 15 &# 39 ;, a second residence chamber 14 &# 39 ;, and finally through a third 6 element drop conditioner 15 &# 34 ;. the drop conditioners were 0 . 602 inch i . d . mixers whose elements had an l / d ratio of 1 . 5 to 1 . 0 . the residence chambers were 3 inch i . d . by 11 inches long . ______________________________________total flow rate 2 / 06 gpmmixer velocity 2 . 31 fpso / a ratio 3 . 06 to 1phase continuity organicinterfacial tension 18 . 0 dynes / cmexit temperature 35 ° c . residence time in system 20 sec . settler 500 ml separatory funnel______________________________________ a sample of the above aqueous solution which had previously been cycled through a standard extraction process was found to have 95 ppm organic entrained in it . measurement was made by infrared spectrophotometry as in previous examples . this aqueous sample was then passed through the apparatus shown in fig6 . the amount of organic entrained in an aqueous sample after 10 minutes of settling time was measured to be only 41 ppm , a reduction in entrainment of 56 %. the effect of employing one or more parallel horizontally oriented baffles in a settler was investigated to determine the improvement in phase separation time and the reduction in entrainment of the organic phase in the aqueous phase . in this test , the two phases were passed through a 48 element , 1 / 2 &# 34 ; inside diameter mixer , followed by a settler chamber having a 3 &# 34 ; inside diameter and a 10 foot length . two test set - ups were employed as illustrated respectively in fig7 a and 7b in which the settler tube is identified by the reference numeral 40 , the baffles are identified by the reference numeral 42 , and the mixer is identified by the reference numeral 45 . fig7 a shows the 3 &# 34 ; diameter settler 40 leading abruptly from the mixer 45 while fig7 b shows the insertion of a conical transition stage 46 between the mixer 45 and the settler 40 . fig7 b corresponds to apparatus used in test 59 , as identified in table iii , in which only a single baffle 42 was employed . kerosene was employed as the organic phase while water was the aqueous phase . entrainment was measured by the same infrared spectrophotometry technique as in the previous examples . the organic was run as the continuous phase , and the average temperature was 25 ° c . table iii__________________________________________________________________________ flow area settler mixer rate ratio total residence entrainmenttest velocity o / a gpm settler / test baffle time from exitno . ( fps ) mixer total mixer time configuration ( min .) sample lppm__________________________________________________________________________55 2 . 70 3 . 2 / 1 1 . 70 36 / 1 35 baffles 0 °; 2 . 2 94 12 &# 34 ; from entrance56 1 . 92 3 . 2 / 1 1 . 20 36 / 1 32 baffles 0 °; 3 . 0 26 12 &# 34 ; from entrance57 2 . 70 3 . 2 / 1 1 . 70 36 / 1 40 no baffle 2 . 2 13158 1 . 90 3 . 3 / 1 1 . 18 36 / 1 30 &# 34 ; 3 . 0 3459 2 . 70 3 . 2 / 1 1 . 70 36 / 1 29 30 ° smooth 2 . 2 105 transition ; single 0 ° baffle__________________________________________________________________________ the employment of the baffles 42 horizontal to the flow of the dispersed phases in the settling chamber 40 , and spaced 12 inches from the entrance , as defined in test 55 and 56 resulted in a reduction in entrainment of about 30 % from that of tests 57 and 58 in which the baffles 42 were not employed . in test 59 , the 30 ° conical section 46 was employed as shown in fig7 b , but only a single baffle 42 was used , resulting in a reduction of entrainment as compared to test 57 of approximately 20 %. it was therefore concluded that the employment of baffles as above defined in the settler substantially enhanced the reduction of entrainment with a corresponding reduction in residence time within the settler . while the methods and apparatus herein described constitute preferred embodiments of the invention , it is to be understood that the invention is not limited to these precise apparatus and methods , and that changes may be made in either without departing from the scope of the invention , which is defined in the appended claims .