Selective separation and recovery of iron and tin from high calcium type tin- and iron-bearing tailings using magnetizing roasting followed by magnetic separation

Sn recovery from a tin-bearing middling with a high iron content and the transformation behaviours of the associated As, Pb, and Zn

A tin-bearing middling with high Fe and low SiO₂ contents is generated from the beneficiation of tin-bearing tailings. The middling is composed of valuable Sn and Fe metals and harmful Pb, Zn, and As elements, which can cause severe economic and environmental issues if left on land for extended periods. This study proposed a new two-step process for the treatment of the middling, which includes oxidising roasting followed by sulfurization roasting. The results demonstrate that Sn, Pb, Zn, and As were volatilised efficiently and concentrated in the collected dust while concentrated Fe remained in the roasted residue. During the sulfurization roasting process, CaSO₄ that originated from the middling played a major role in Sn sulfurization and volatilisation through its transformation to SO₂ (g). Furthermore, CO₂ (g) positively affected separation of Sn and As from FeSn and FeAs alloys, respectively, via the selective oxidation of the Fe component in the alloy phases. Under optimal conditions, the Sn recovery reached 97.5%, and the residual contents of As, Pb, and Zn decreased to 0.055, 0.013, and 0.13 wt%, respectively. This study aids in the resource utilisation of tin-bearing middling and is of substantial significance for the quantitative reduction of tin-bearing tailings.

A value-added multistage utilization process for the gradient-recovery tin, iron and preparing composite phase change materials (C-PCMs) from tailings

Tin-, iron-bearing tailing is a typically hazardous solid waste in China, which contains plenty of valuable tin, iron elements and is not utilized effectively. In this study, a multistage utilization process was put forward to get the utmost out of the valuable elements (tin and iron) from the tailings, and a gradient-recovery method with three procedures was demonstrated: (1) An activated roasting followed by magnetic separation process was conducted under CO-CO2 atmosphere, tin and iron were efficiently separated during magnetic separation process, and 90.8 wt% iron was enriched in magnetic materials while tin entered into non-magnetic materials; (2) The tin-enriched non-magnetic materials were briquetted with CaCl2 and anthracite and roasted, then tin-rich dusts were collected during the chloridizing roasting process; (3) The roasted briquettes were infiltrated in melting NaNO3 to prepare NaNO3/C-PCMs by a infiltration method. Three kinds of products were obtained from the tailings by the novel process: magnetic concentrates containing 64.53 wt.% TFe, tin-rich dusts containg 52.4 wt.% TSn and NaNO3/C-PCMs for high temperature heat storage. Such a comprehensive and clean utilization method for tin-, iron-bearing tailings produced no secondary hazardous solid wastes, and had great potential for practical application.

Measuring the sustainability of tin in China

Tin is a component of many items used in daily activities, including solder in consumer electronics, tin can containing food and beverages, polyvinyl chloride stabilizers in construction products, catalysts in industrial processes, etc. China is the largest producer and consumer of refined tin, and more than 60% of this refined tin is applied in the electronics sector as solder. China is the leader in global economic growth; simultaneously, China is also a major producer and consumer of electrical and electronic equipment (EEE). Thus, future tin supply and demand in China are forecasted, based on the gross domestic product per capita and the average consumption of refined tin in past five years. Current tin reserves and identified resources in China can meet the future two decades of mine production, but import of tin will also be critical for China's future tin consumption. However, there will be a lot of uncertainty for import of tin from other countries. At the same time, virgin mining of geological ores is a process of high energy consumption and destruction of the natural environment. Hence recycling tin from Sn-bearing secondary resources like tailings and waste electrical and electronic equipment (WEEE) can not only address the shortage of tin mineral resources, but also save energy and protect the ecological environment.

Formation mechanisms of Fe3-xSnxO4 by a chemical vapor transport (CVT) process

Our former study reported that Fe-Sn spinel (Fe_3-xSn_xO₄) was easily formed when SnO₂ and Fe₃O₄ were roasted under CO-CO₂ atmosphere at 900-1100 °C. However, the formation procedure is still unclear and there is a lack of theoretical research on the formation mechanism of the Fe-Sn spinel. In this work, the reaction mechanisms between SnO₂ and Fe₃O₄ under CO-CO₂ atmosphere were determined using XRD, VSM, SEM-EDS, XPS, etc. The results indicated that the formation of Fe_3-xSn_xO₄ could be divided into four steps: reduction of SnO₂ to solid phase SnO, volatilization of gaseous SnO, adsorption of gaseous SnO on the surface of Fe₃O₄, and redox reaction between SnO and Fe₃O₄. During the roasting process, part of Fe³⁺ in Fe₃O₄ was reduced to Fe²⁺ by gaseous SnO, and meanwhile Sn²⁺ was oxidized to Sn⁴⁺ and entered into Fe_3-xSn_xO₄. The reaction between SnO₂ and Fe₃O₄ could be summarized as Fe₃O₄ + xSnO_(g) → Fe_3-xSn_xO₄ (x = 0-1.0).