Tin-bearing middling, a hazardous solid waste produced during beneficiation of tin deposits and tin-bearing tailings, presents a serious environmental pollution risk due to high levels of As. This paper aims to explore an environmentally friendly technology to reduce toxic substances and prepare a high value-added bronze material from tin-bearing middling. The co-process for tin-bearing middling, anthracite , and copper is first proposed at 1073–1123 K. Variables like temperature, amount of added anthracite, and holding time were optimized. Those results showed that 95.56% Sn and 92.79% As were recovered; levels of Fe in the residue reached 73.52 wt%. During roasting, SnO 2 in the tin-bearing middling was initially transformed into SnO(g), then into an Fe–Sn spinel (Fe 3-x Sn x O 4 ) and Ca 2 SnO 4 , and finally a Cu–Sn alloy. Generation of the Fe–Sn spinel came primarily from substitution of Fe 2+ by Sn 2+ , but small amounts of Sn 4+ replaced Fe 3+ in Fe 3 O 4 . Meanwhile, FeAsS and FeAsO 4 were initially transformed into As 4 (g) and then solidified as a Cu–As alloy. Interestingly, the residual As existed as Fe–As alloy, but As leaching levels did not exceed 0.02 mg/L. After initial treatment, the Cu alloy can be prepared for bronze. Meanwhile, subsequent volatilization and solidification of As resulted in a significant reduction of arsenic-bearing waste that minimizes environmental risk.
The high-temperature volatilization behavior of the SnO–SiO 2 and SnO–CaO–SiO 2 slag systems was studied by simultaneous thermal analysis. The volatilization characteristics of the two systems with different SnO contents and different heating rates were discussed, and the kinetic parameters, reaction mechanism, and thermodynamic parameters of the volatilization reaction of the slag system at high temperature were calculated. The results of thermal analysis show that the volatilization of tin slag at high temperature is related to the activity of SnO and the decomposition of stannous silicate in tin slag. The slag system has obvious volatilization effect when the content of SnO is more than 60% in the SnO–SiO 2 binary slag system. When CaO is added into the binary slag system, the volatilization of slag system becomes easier. The volatilization rate decreases with increasing heating rate. The volatilization kinetic parameters and mechanism functions of the SnO–SiO 2 and SnO–CaO–SiO 2 systems were calculated by Coats–Redfern and Achar–Brindley–Sharp–Wendworth methods. It is concluded that the volatilization of tin slag at high temperature is controlled by three-dimensional diffusion mechanism. The mechanism function is Jander equation with integral form of [1 − (1 − α ) 1/3 ] 2 and the differential form of 3/2(1 − α ) 2/3 [1 − (1 − α ) 1/3 ] −1 . The rate constants of the SnO–SiO 2 and SnO–CaO–SiO 2 systems are \(k\, = \,1.36\, \times \,10^{16} \,\exp \,\left( {{{ - \,61408.61} \mathord{\left/ {\vphantom {{ - \,61408.61} T}} \right. \kern-\nulldelimiterspace} T}} \right)\) and \(k\, = \,1.61\, \times \,10^{17} \,\exp \,\left( {{{ - \,64869.66} \mathord{\left/ {\vphantom {{ - \,64869.66} T}} \right. \kern-\nulldelimiterspace} T}} \right)\) , and the isokinetic temperatures are 1174.4 and 1208.3 °C, respectively. Finally, the thermodynamic parameters of the slag system in the high-temperature volatilization process are discussed. The activation enthalpy ΔH of the SnO–SiO 2 and SnO–CaO–SiO 2 systems is 498.33 and 526.96 kJ/mol, respectively. The activation Gibbs free energy ΔG is 436.56 and 433.87 kJ/mol, and the activation entropy ΔS is 42.66 and 62.84 J/(mol K), respectively. Graphical Abstract
危险品化学品经营许可证（带存储）