Clean and sustainable elimination of arsenic–aluminum slag from smelted crude tin via vacuum volatilization – Fractional condensation

Abstract

In high–tech industries, Sn is an indispensable strategic metal. However, the pyrometallurgical refining process of crude Sn is marred by the production of a substantial amount of hazardous solid waste, primarily As–Al slag, which poses a direct threat to the ecological safety of production areas. To address this problem, this study developed a novel process for that eliminates As–Al slag from a source of crude Sn by employing a vacuum volatilization – fractional condensation process, which was validated by theoretical calculations and laboratory experiments. Theoretically, at system pressures in the 1–10 Pa, the initial volatilization temperatures of Sn, Sb, and As vary significantly. However, the formation of intermetallic compounds can induce the volatilization of Sn. Experimentally, the condensation temperature for Sb was predominantly between 603 K and 810 K, and that for As was between 331.7 K and 484.7 K, which are significantly different ranges. Under optimal experimental conditions, the separation rate of Sb in the Sn–Sb alloy was 93.92%, and the resultant Sn product contained 0.0143% Sb. During the volatilization of the Sn–As alloy, the presence of Sn4As3 compounds impeded the volatilization of As; hoewver, the As content in the Sn product was 0.0053%. In the directional condensation of the As–Sb alloy, the condensation temperatures for As and Sb were similar to those of the pure metals, yielding As and Sb products with purities of 99.99% and 99.95%, respectively. Industrial production trials treating HACT via a continuous vacuum separation – intermittent vacuum separation process achieved direct recovery rates of 72.99% for Sn and 71.15% for Sb, with a total energy consumption as low as 1086 kWh/t. Similarly, the treatment of LACT via a multi–stage continuous vacuum separation process yielded residues that satisfied production standards at a treatment cost of 1187 RMB/t. This entire process requiresno additives, and substantially mitigates the generation of As–Al slag at the source.