Efficient recovery of copper, lead and zinc from heavy metal gypsum residue and zinc-containing fume by synergistic sulfidation-acid leaching

Abstract

In this study, a synergistic sulfidation-acid leaching process was proposed to recover valuable metals from gypsum residue and zinc-containing fume. The equilibrium phase composition of the sulfidation reaction and calculations of the thermodynamic stability region show that 89.36% Zn, >99% Pb and >99% Cu of gypsum residue and zinc-containing fume can be sulfured to ZnS, PbS and Cu2S, under sufficient sulfur partial pressure, low oxygen partial pressure and 400 −1000 ℃. Sulfidation roasting experiments show that the sulfidation rate of Cu, Pb and Zn reach 81.43%, 88.25% and 92.31%, respectively, under the roasting conditions of material mass ratio of 30 g:10 g, carbon dosage of 3.75 g, roasting temperature of 800 ℃ for 3 h. E−pH plots show that ZnS, PbS and Cu2S can be enriched in the leaching residue, under leaching conditions at 25 ℃, pH<4 and −0.4 V<φ(E)<0.04 V. The leaching experiments showed that the sulfide is retained in the leaching residue, while the leaching rates of Cu, Pb and Zn are 1.94%, 2.05% and 1.51%, respectively, under the conditions of 25 ℃, CHCl of 0.5 mol/L, L/S of 5 mL/g, stirring rate of 300 r/min, and stirring time of 30 min. This study provides a new approach for the synergistic disposal of gypsum residue and zinc-containing fume.

1. Introduction

Zinc-containing fume is an important hazardous solid waste, mainly including iron and steel fume, zinc hydrometallurgical leaching residue, blast furnace and electric arc furnace smelting dust, which usually contains a large number of precious metal elements and toxic elements such as Ge, In, Sn, Ag, Pb, Fe, As, Cd and other elements [1−3]. The traditional landfill method of disposing zinc-containing fume not only wastes resources, but also leads to the accumulation of toxic elements in the soil and groundwater, which seriously affects the sustainable development of human beings, animals and plants [4−6]. In the context of global efforts to develop clean, low-carbon industrial strategies, the resourceful use of zinc-containing fume ash is imminent.

In general, the main methods of treating zinc-containing fumes are pyrometallurgy and hydrometallurgy [7−9]. The hydrometallurgical process mainly uses inorganic acids such as hydrochloric, nitric and sulfuric acids to leach metal oxides from zinc-containing fumes, which has the advantage of high metal recovery [10−12]. However, this process usually requires the addition of oxidizing agents and high acidity, which tends to cause secondary environmental pollution and dissolve Na, Mg, Fe and other impurity elements, leading to difficulties in the subsequent separation of valuable metals and complex wastewater treatment [13, 14]. For example, XIN et al [15] used a sulfuric acid + ozone system to leach 95.79% Zn, about 37% Si, about 14% Al and about 7% Fe from zinc oxide dust. XU et al [16] extracted more than 95% of Zn, 89% of Ge, about 40% of Si, about 18% of Al, and about 7% of Si under the ultrasonic assisted system of H2SO4+ (NH4)2S2O8. The pyrometallurgical process is the conversion of the metal compounds in zinc-containing fume into metal monomers under carbon-reducing conditions above 1000 ℃ [17, 18]. It has the advantages of large processing scale, strong adaptability of raw materials, and separation of other elements from metal Zn can be achieved through high temperature evaporation [19]. The disadvantages are high energy consumption, low product purity and high CO emission [11, 20, 21]. In response to the technical challenges and limitations faced by single treatment technologies, the development of a clean, environmentally friendly and economical combined fire-wet process has become a research hotspot for the high-value utilization of zinc-containing fume and dust [22].