Process for concentrating lead and silver by flotation in products which contain oxidized lead
BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of the process disclosed, in which the silver and lead are floated independently. 
     FIG. 2 is a diagram of the process in which the silver and lead are floated together. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     As shown in FIG. 1, the residues 1 obtained from an electrolytic zinc plant are inserted in a conditioner 2 where part or all of the collectors are added. From here, these residues pass on to a &#34;rougher&#34; stage 3, where the silver, sulphur and zinc, but not the lead, are floated with no sulphurizing agents. For this, collectors are added which do not float the lead; this stage furthermore takes place in an acid medium. The floated product 4 is subjected to a recleaning operation, in two stages 5 and 6 in the case disclosed, to finally obtain a concentrate 7 rich in silver. During the recleaning operations, it is advisable to keep the acid medium between a pH of 2 and 4.5. The residues of the recleaning stages 5 and 6 can be discarded as tailings, as mentioned with reference 8, or be added, as shown with reference 9, to the conditioner 2. 
     It is also possible to add the residues of each recleaning stage at the head of the previous one. 
     Finally, the residue of the recleaning stages 5 and 6 can be added, as shown with reference 10, to the residues 11 of the &#34;rougher&#34; stage 3. During the process disclosed, frothing products can be added, but preferably these products should not have collector properties. 
     The residues 11 pass to the conditioner 12 where a sulphurizing agent is added, preferably sodium sulphide, designed to activate the lead sulphate. The residues treated in this way are subjected to a &#34;rougher&#34; stage where suitable collectors, such as xanthates and/or dithiophosphates are added, to float the lead. The floated product 14 is recleaned in two stages 15 and 16, in the present case, finally obtaining a concentrate rich in lead 17. 
     The residues 18, 19 and 20 of stages 16, 15 and 13 can be disregarded as sterile. The residues 18 and 19 can be added, as shown with reference 21, to the conditioner 12. 
     The residues 11 of the &#34;rougher&#34; stage 3, can be subjected, before the addition of the sulphurizing agent in 12, to a flotation stage 22, whose residue 23 will be that which passes to the conditioner 12, whereas the product floated 24 passes to the conditioner 2. 
     For their part, the residues 20 of the &#34;rougher&#34; stage 13, can also pass on to a flotation stage 25 giving some sterile residues 26 and a floated product 27 which passes to the conditioner 12. 
     The sulphurizing agent, collectors and frothing agents can be added gradually in different points of the relevant circuit. 
     In the case of FIG. 2, in the conditioner 2, apart from the afore-mentioned agents, a sulphurizing agent is added, preferably sodium sulphide, so that in the &#34;rougher&#34;  3&#39;, apart from the silver, sulphur and zinc, the lead also floats. The floated product 4&#39; is subjected to recleaning 5&#39; and 6&#39;, obtaining a concentrate 7&#39; rich in silver and lead. The residues 8&#39; and 11&#39; can be discarded as tailings, or pass the residues 8&#39; as shown with reference 9&#39;, to the conditioner 2. For their part, the residues 11&#39; can be subjected to a floatation operation 22&#39; which will give a tailings residue 23&#39; and a floated product 24&#39; which passes to the conditioner 2. 
     During the process, collector and frothing agents are added, as also can be sulphurizing agents, in several stages throughout said process.