Pretreatment of Se-Containing Lead Matte by Alkaline Pressure Leaching

Se-containing lead matte has so far not been efficiently treated for recovering valuable elements. In this study, a two-stage method has been developed for processing lead matte. The first stage is the pretreatment of lead matte by alkaline pressure leaching. It is shown that NaOH solution was the most efficient for lead-matte pressure pretreatment, compared with Na2CO3 solution or NaOH + Na2CO3 mixed solution. Furthermore, the effects of various experimental parameters on pressure pretreatment were investigated, including the concentration of NaOH, the temperature at which oxygen is introduced, oxygen partial pressure, liquid-to-solid ratio, stirring rate, and time. It was observed that the concentration of NaOH played a key role in maximizing the extractions of S and Se while minimizing the dissolution of Pb and As and leaving them in the solid residue. Optimal pressure pretreatment was achieved under the following conditions: NaOH concentration 110 g L−1, oxygen introduction temperature 125 °C, oxygen partial pressure 0.4 MPa, liquid-to-solid ratio 4:1, and time 1.5 h. The average extractions of S, Se, Pb, and As under this condition were 98.07, 96.83, 4.09, and 0.42%, respectively. The second stage is the atmospheric pressure acid leaching of the alkaline-pretreated solid residue. Very high extractions of Cu (>99%) and low leaching ratios of Fe (2.81%) and As (2.66%) were achieved. The advantages of this two-stage method include (1) effective separation and recycling of valuable elements Se, S, and Cu; (2) low energy consumption due to heat produced by exothermic reactions of sulfides’ oxidation; and (3) little waste being produced. Overall, the alkaline pressure pretreatment is not only suitable for the separation of S and Se from Se-containing lead matte, it can also produce simple oxidized copper residues for producing copper sulfate solution by atmospheric acid leaching, having the potential for simplifying the downstream electrodeposition for the recovery of high-purity copper