Combined hydro-pyrometallurgical method for the recovery of high lead/tin/bronze alloy from industrial scrap

Abstract

The major item of concern of this work was to recover bronze alloys meeting DIN 1617 as specified applying combined hydrometallurgical and pyrometallurgical treatments. The hydrometallurgical leaching process utilizes hydrogen peroxide in ammonia to dissolve copper selectively. Lead and tin are then leached with hydrochloric acid in hot conditions. Lead chloride precipitates by cooling. Lead chloride so leached is converted into carbonate by leaching with sodium carbonate solution. Copper, lead and tin metals are recovered from the leach products by thermal reduction. Pyrometallurgical treatment involves melting with a carbon/alkali borate flux at 1150–1300°C for controlling slag quantity. Parameters affecting the recovery efficiency of the investigated methods, such as time, temperature, hydrogen peroxide concentration, and stoichiometric ratio of the leachants are given. Results obtained show that melting of bronze turnings failed to recover standard bronze alloys due to thermal volatilization of tin and escape of lead into the slag. Combined hydrometallurgical processes are significant for recovering metals as well as bronze alloys from the turnings. Hydrogen peroxide assists dissolution of the metals originally present in the scrap. Metals entering the slag are recycled in the same manner. Free metals are recovered from the leached products by thermal reduction with hydrogen or spent active carbon. The activation energy of the latter process amounts to 83.6, 12.7 and 51.73 kJ/mol for copper, lead and tin respectively. The maximum recovery efficiency of the suggested method amounts to 98.7%. A preliminary economic evaluation suggests that the process could be economically feasible.