Leaching-Electrowinning Process Of Extraction Of Metallic Lead From Lead Bearing Wastes And Low-grade Lead Oxide Ore

A huge quantity of lead-bearing wastes,which is classified as hazardous wastein most countries,has been generated in the industries such as hydrometallurgicalprocess of zinc,batteries manufacture,and chemical process．In general,the contentsof lead in the wastes may be quite low and usually are disposed of at dumping sites．In addition,thousands of millions of tailings containing low grade lead are also beingstored at the dumping sites in the mining plants．The concentration of lead from thesesecondary resources may be quite difficult and their recycling as raw materials hasbeen limited due to the unavailability of cost-effective technologies．Pyrometallurgical process may be one option for the lead extraction from the wastes,but its lead dust pollution has caused environmental constraints．Considering thedissolution of lead in the alkaline solution,a cleaner hydrometallurgical process usingalkaline leaching and electrowinning had been developed for the extraction of leadfrom the wastes and low-grade lead ores in this work．Thermodynamics of alkaline leaching of lead was calculated．The solubility oflead in 5 mol·L^-1 NaOH solution at 25℃was observed to be 25．56 g·L^-1．Meanwhile,the E-pH diagrams of Pb-H₂O,PbS-H₂O,Pb-SO₄^-2--H₂O and Pb-CO₃^2--H₂O systemswere calculated and plotted．It was found that PbO,PbSO₄ and PbCO₃ can bedissolved in concentrated NaOH solutions while the dissolution of PbS may benegligible．Leaching kinetics of lead oxide ore and lead bearing wastes in NaOHsolution were also investigated．The leaching of lead oxide may be controlled bydiffusion of NaOH solution passing through the solid phase layer at lowertemperature and less NaOH concentration,and by surface chemical reaction at hightemperature and high NaOH concentration．Generallyï¼›lead bearing wastes can bemore easily and quickly leached than lead oxide ores did．Electrode reaction kinetics of lead electrodeposition from NaOH solution wasstudied by cyclic voltammetry．The reduction of lead occurs entirely through thecomplex species Pb(OH)₃^- but not Pb²⁺．The catholic reaction is a quasi-reversible process controlled by mass transfer with a diffusion coefficients of 1．15×10^-6 cm²Â·s^-1．Lead electrodeposition potential shifts towards negative values as the decrease of Pbconcentration and the increase of scanning rate,NaOH concentration and temperature．Anodic process is mainly the oxygen evolution reaction,but lead complex in thesolution will be oxidized to PbO₂,Pb₃O₄ and PbO₃^2- in the anode．The oxidizationrate decreases as the increase of NaOH concentration and the decrease of Pbconcentration and the temperature．The effects of several parameters including lead concentration,temperature,current density,NaOH concentration,electrode distance and electrode material oncurrent efficiency and energy consumption of lead electrodeposition wereinvestigated．The optimum conditions were 20 g·L^-1 of lead concentration,5 g·L^-1 oflead concentration left in the electrolyte,50℃of temperature,400 A·m^-2 of currentdensity,5 mol·L^-1of NaOH concentration,and stainless steel of electrode material．Equilibrium potential of Zn,As,Sb,W,Cu and Sn electrodeposition fromNaOH solution is calculated．The effects of impurities in the solution on leadelectrodeposition process were studied by cyclic voltammetry and electrowinningmethods．The results show that relatively high zinc concentration in the solution hasno effect on the lead electrodeposition process．Copper in the solution must bepurified before lead electrodeposition because it will be electrodeposited prior to leadin the cathode．Tin,C₄H₄O₆^2-,C₂O₄^2- and glutin in the solution decrease the currentefficiency of the lead electrodeposition process,while As,Sb and W,as well asPO₄^3-,SO₄^2-,SO₃^2-,SiO₃^2-,SCN^-,CO₃^2-,Cl^- and AC^- have no influence．Cu can be removed from the leaching solution by Pb power replacement．Theoptimum condition is Pb／Cu ratio of 2:1,reaction time of 15 min,temperature of:30℃．Na₂S and CaO were used to remove impurities,and found all the Cu,Cd,Pb andmost Mn,Zn,W,Sb,and Sn in the leaching solution can be removed．Addition ofCaO can co-deposit part of Sb and Sn．The lead production flowsheet using lead oxide ore and lead bearing wastes andthe process of comprehensive recovery of lead and zinc from lead and zinc bearingwastes were put forward based on the bench-scale results．The purity of lead thusprepared can be over 97ï¼…,with an energy consumption below 0．7 kWh·kg^-1． Pilot-scale project was also designed．It has been concluded that the processdeveloped in this work is cost-effective．...