Improved extraction of acid-insoluble monosulfide minerals by stannous chloride reduction and its application to the separation of mono- and disulfide minerals in the presence of ferric iron

Han Ye; Kun Gao; Guining Lu; Yingying Xie; John R Reinfelder; Weilin Huang; Xueqin Tao; Xiaoyun Yi; Zhi Dang

doi:10.1016/j.scitotenv.2021.147367

Improved extraction of acid-insoluble monosulfide minerals by stannous chloride reduction and its application to the separation of mono- and disulfide minerals in the presence of ferric iron

Sci Total Environ. 2021 Sep 1:785:147367. doi: 10.1016/j.scitotenv.2021.147367. Epub 2021 Apr 27.

Authors

Han Ye¹, Kun Gao¹, Guining Lu², Yingying Xie³, John R Reinfelder⁴, Weilin Huang⁴, Xueqin Tao⁵, Xiaoyun Yi⁶, Zhi Dang⁷

Affiliations

¹ School of Environment and Energy, South China University of Technology, Guangzhou 510006, China.
² School of Environment and Energy, South China University of Technology, Guangzhou 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou 510006, China. Electronic address: lutao@scut.edu.cn.
³ School of Chemistry and Environmental Engineering, Hanshan Normal University, Chaozhou 521041, China.
⁴ School of Environmental and Biological Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA.
⁵ College of Resources and Environment, Zhongkai University of Agriculture and Engineering, Guangzhou 510225, China.
⁶ School of Environment and Energy, South China University of Technology, Guangzhou 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou 510006, China.
⁷ School of Environment and Energy, South China University of Technology, Guangzhou 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou 510006, China; Guangdong Provincial Key Laboratory of Solid Wastes Pollution Control and Recycling, South China University of Technology, Guangzhou 510006, China. Electronic address: chzdang@scut.edu.cn.

PMID: 33940422
DOI: 10.1016/j.scitotenv.2021.147367

Abstract

Metal sulfides, which are important indicators of sulfur cycling, are usually divided into two categories according to sulfur chemical valence: (1) monosulfides (S^2-) and (2) disulfides (S₂^2-). The two sulfur species are separated and quantified by a sequential-extraction method. Specifically, monosulfides are extracted as acid-volatile sulfide (AVS) using 6 M HCl prior to the extraction of disulfides using acidic CrCl₂, which is defined as chromium-reducible sulfur (CRS). However, the conventional AVS procedure does not result in the quantitative extraction of S^2- from the acid-insoluble metal monosulfide, copper sulfide (CuS). Consequently, residual sulfur in CuS (CuS-S) may be extracted as CRS resulting in the inaccurate separation of these two sulfur species. In this study, we used stannous chloride (SnCl₂) to improve CuS-S recovery in the AVS procedure and permit the separate extraction of sulfur from CuS and pyrite (FeS₂), the most abundant disulfide in nature. Our results show that the addition of SnCl₂ increased the recovery of CuS-S as AVS from less than 36% to as high as 92% in the absence of pyrite and Fe³⁺ and 89% in the presence of pyrite and Fe³⁺. In addition, based on the observed correlation between the concentration of SnCl₂ and the dissolution of FeS₂, we identified the appropriate concentration of SnCl₂ needed to avoid the dissolution of FeS₂ in the AVS procedure. SnCl₂ also minimized the oxidation of CuS-S by Fe³⁺ released from ferric minerals during the extraction of AVS. Based on the results of a series of sequential-extraction experiments, we show that an amendment of SnCl₂ in the AVS procedure followed by CRS permits the quantitative separation of CuS-S and FeS₂-S while also preventing interference by Fe³⁺. Our method will find application in research concerned with the fate of metals and the biogeochemistry of sulfur in the environment.

Keywords: Acid-volatile sulfide; Copper sulfide; Metal sulfides; Pyrite; Sequential extraction; Stannous chloride.