A green process for arsenic removal and tungsten recovery from tungsten residue waste: Focused on the separation and recovery of arsenic and tungsten via solvent extraction followed by H2S precipitation

Tungsten residue waste (TRW) has been recognized as a hazardous solid waste by Chinese government due to its high As content and leaching toxicity. This paper presents a green full process for efficient arsenic removal and tungsten recovery from hazardous TRW, focusing on the separation and recovery of arsenic and tungsten from leach solution of TRW via solvent extraction with N235 followed by H2S precipitation. The results showed that the W recovery was nearly 100% and As, Si, S removal was 96.68%, 86.93% and 99.73%, respectively, under optimized conditions. Most of the As(III) is extracted in the organic phase as H3AsO3 through hydrogen bonding. During the oxidative scrrubbing process, most of As(III) was oxidized to As(V) and scrubbed. As(V) in the scrubbed organic phase mainly existed in the form of [As2W18O62](6-). The arsenic (similar to 26 g/L) in the raffinate was then completely removed by sulfide precipitation with 99.6% of As precipitation. The arsenic precipitation slag was a mixture of As2S3 and S with a mole ratio close to 1:1. The arsenic precipitation mother liquor was first cooled and crystallized, followed by causticization with lime to a NaOH concentration of 70 g/L, which can be used for the leaching of hazardous TRW. A green process of TRW harmless treatment and W recovery was proposed, and the flow of As and W in the process was analyzed. The closed-loop strategy shows great promise for the harmless treatment and tungsten recovery of TRW on an industrial scale to promote circular economy and environmental protection.