Reclaiming of lead in form of high purity lead compound from recovered electrode paste slime of dismissed lead batteries and/or of lead minerals

Abstract

An all-wet process for reclaiming the lead content of impure electrode paste or slime from discarded lead batteries and/or lead minerals, in form of high purity lead compound, comprises a) suspending the impure lead containing material in a lead sulphate dissolving aqueous solution of a salt belonging to the group composed of the acetates of sodium, potassium and ammonium; b) adding to the suspension sulphuric acid in an amount sufficient to convert all lead oxides to lead sulphate soluble in the acetate salt solution and slowly adding to the suspension either hydrogen peroxide or a sulphite or bubbling sulphurous anhydride through it, in a measure adapted to reduce any lead dioxide to lead oxide converted eventually to soluble lead sulphate by the sulphuric acid; c) separating a limpid acetate salt solution containing dissolved lead sulphate from a solid phase residue including all undissolved compounds and impurities; d) adding to the separated solution of lead sulphate either carbonate or hydroxide of the same cation of the acetate salt of the lead sulphate dissolving solution for precipitating highly pure lead carbonate/oxycarbonate or lead oxide or hydroxide, respectively, while forming sulphate of the cation, soluble in the acetate salt solution; and e) separating the precipitated high purity lead compound from the acetate salt solution now containing also sulphate of the same cation of the acetate salt. The acetate salt solution containing also sulphate of the same cation of the acetate salt separated from the precipitated compound of lead is re-cycled to step a) and the content of sulphate of the same cation in the solution is maintained below saturation limit by continuously or periodically cooling at least a portion of the solution separated from the precipitated lead compound to cause selective crystallization of sulphate salt of the same cation of the acetate salt and removing it as a by-product. Optionally, the separated solid phase comprising insoluble compounds of lead and/or undissolved concretions of lead compounds is treated in hot concentrated hydroxide of the same cation of the selected acetate salt and converting these compounds of lead and/or undissolved concretions of lead compounds to soluble plumbites, and the separated lead containing alkaline liquor may be added to the limpid acetate solution for precipitating all reclaimable lead in form of high purity lead oxide or hydroxide.

1 . A process for reclaiming the lead content of impure electrode paste or slime from discarded lead batteries and/or lead minerals, in form of high purity lead compound, comprising the steps of
 a) suspending the impure lead containing material in a lead sulphate dissolving aqueous solution of a salt belonging to the group composed of the acetates of sodium, potassium and ammonium;   b) adding to the suspension sulphuric acid in an amount sufficient to convert all lead oxides to lead sulphate soluble in the acetate salt solution and slowly adding to the suspension either hydrogen peroxide or a sulphite or bubbling sulphurous anhydride through it, in a measure adapted to reduce any lead dioxide to lead oxide converted eventually to soluble lead sulphate by the sulphuric acid;   c) separating a limpid acetate salt solution containing dissolved lead sulphate from a solid phase residue including all undissolved compounds and impurities;   d) adding to the separated solution of lead sulphate either carbonate or hydroxide of the same cation of the acetate salt of the lead sulphate dissolving solution for precipitating highly pure lead carbonate/oxycarbonate or lead oxide or hydroxide, respectively, while forming sulphate of the cation, soluble in the acetate salt solution;   e) separating the precipitated high purity lead compound from the acetate salt solution now containing also sulphate of the same cation of the acetate salt.   
     
     
         2 . The process of  claim 1 , wherein said acetate salt solution containing also sulphate of the same cation of the acetate salt separated from the precipitated compound of lead is re-cycled to step a) and the increasing content of sulphate of the same cation in the solution is maintained below saturation limit by continuously or periodically cooling at least a portion of the solution separated from the precipitated lead compound to cause selective crystallization of sulphate salt of the same cation of the acetate salt and removing it as a by-product. 
     
     
         3 . The process of  claim 2 , wherein prior to cooling for selectively precipitating sulphate salt of the same cation of the acetate salt, the solution is contacted with a chelating resin adapted to sequester any residual lead ions from the solution for selectively precipitating substantially lead-free sulphate salt of the same cation of the acetate salt, upon cooling. 
     
     
         4 . The process of  claim 1 , wherein the selective dissolution of the lead sulphate is carried out by suspending the impure material in an aqueous solution of sodium acetate having a concentration comprised between 10 g and 120 g of salt in 100 g of water at a temperature comprised between 20° C. and boiling point, for a stirring time comprised between 5 and 180 minutes. 
     
     
         5 . The process of  claim 1 , wherein selective dissolution of the lead sulphate is carried out by suspending the impure material in an aqueous solution of ammonium acetate having a concentration comprised between 20 g and 120 g of salt in 100 g of water at a temperature comprised between 20° C. and boiling point, for a stirring time comprised between 5 and 180 minutes. 
     
     
         6 . The process of  claim 1 , wherein selective dissolution of the lead sulphate is carried out by suspending the impure material in an aqueous solution of potassium acetate having a concentration comprised between 20 g and 120 g of salt in 100 g of water at a temperature comprised between 20° C. and boiling point, for a stirring time comprised between 5 and 180 minutes. 
     
     
         7 . The process of  claim 1 , further comprising suspending said separated solid phase residue including all undissolved compounds and impurities in hot concentrated hydroxide of the same cation of the selected acetate salt for converting and dissolve compounds of lead or concretions thereof that could not be dissolved in the acetate salt solution in form of plumbite salt of the hydroxide cation, separating a lead plumbite containing alkaline liquor from a solid phase of impurities contained in the starting material and adding the separated lead containing liquor to the separated acetate solution for precipitating all reclaimable lead as highly pure lead oxide or hydroxide. 
     
     
         8 . A plant for reclaiming the lead content of impure electrode paste or slime from discarded lead batteries and/or lead minerals, in form of high purity lead compound, comprising:
 a) a first reactor (RAC ( 1 )) having stirring and heating means for suspending the impure material in a lead sulphate dissolving aqueous solution of a salt belonging to the group composed of the acetates of sodium, potassium and ammonium, means for controlled addition of sulphuric acid and means for controlled addition of a reagent belonging to the group composed of hydrogen peroxide, sodium sulphite and sulphurous anhydride;   b) a first solid-liquid separator (F 1 ) for separating a solid phase constituted by insoluble compounds of lead and/or undissolved concretions of lead compounds and impurities from a limpid acetate salt and lead sulphate solution;   c) a second reactor (RAC ( 2 ), RAC ( 3 ), RAC ( 4 )) adapted to hold the limpid aqueous solution of acetate salt and lead sulphate solution, having stirring and heating means and means for adding to the solution either a carbonate or a hydroxide of the same cation of said acetate salt, for precipitating insoluble carbonate/oxycarbonate of lead or lead oxide or hydroxide, respectively, and forming sulphate of the same cation of the acetate salt, soluble in the aqueous solution;   d) a second solid-liquid separator (F( 2 ), F( 3 ), F( 4 )) for separating the solid phase constituted by said precipitated compound of lead from an aqueous solution of acetate salt now containing also sulphate of the same cation of the acetate salt;   e) means for re-cycling the separated solution to said first reactor (RAC ( 1 ));   f) a third reactor (RAC ( 5 )) having stirring means and means for controlled cooling and/or heating of a continuously or periodically treated portion of said recycling solution for selectively crystallizing sulphate of the same cation of the acetate salt contained in the solution;   g) a third solid-liquid separator (F( 5 )) for separating said crystallized sulphate of the same cation of the acetate salt of said treated portion of recycling solution that is then recycled to said first reactor (RAC ( 1 )).   
     
     
         9 . The plant of  claim 8 , further comprising a column filled with chelating resin, through which said continuously or periodically treated portion of recycling solution is passed for sequestering residual lead ions from the solution, before introducing it in said fourth reactor (RAC ( 5 )) for selectively crystallizing sulphate of the same cation of the acetate salt contained in the solution. 
     
     
         10 . The plant of  claim 9 , further comprising means for periodically stripping sequestered lead ions from said chelating resin by circulating acetic acid through the column and means for introducing the circulated amount of acetic acid to said first reactor (RAC ( 1 )). 
     
     
         11 . The plant of  claim 8 , further comprising a fourth reactor (RAC (2bis)) having stirring and heating means for suspending said separated solid phase comprising insoluble compounds of lead and/or undissolved concretions of lead compounds in hot concentrated hydroxide of the same cation of the selected acetate salt and converting said compounds of lead and/or undissolved concretions of lead compounds to soluble plumbites; a fourth solid-liquid separator (F (2bis)) for separating lead containing alkaline liquor from a solid phase of impurities; and means for introducing the lead containing alkaline liquor into said second reactor (RAC ( 2 ), RAC ( 3 )) for precipitating all reclaimable lead in form of high purity lead oxide or hydroxide. 
     
     
         12 . The plant of  claim 8 , further comprising an oven in which the separated lead compound, if in form of lead carbonate and/or oxycarbonate or hydroxide, is decomposed to lead oxide and carbon dioxide or water, respectively.