Pollution characteristics and source identification of farmland soils in Pb-Zn mining areas through an integrated approach.

Long-term mining activities have caused serious heavy metals contamination of farmland soils. In this study, we investigated the concentrations, distributions, accumulations, potential ecological risk, and sources of eight heavy metals in farmland soils of Pb-Zn mining areas. According to the soil standard GB15618-2018, Cd was the most contaminated, followed by Pb and Zn. The geo-accumulation index showed that Pb, Zn, Cd, and Hg accumulated seriously. The potential risk index indicated that Cd, Hg, and Pb were the main environmental risk elements. An integrated approach combining multivariate statistical analysis, PMF, and GIS mapping was used to analyze the sources of heavy metals. Four main sources were identified and quantified: (1) mining activities source, the main source of Cd (71.09%) and Zn (61.88%); (2) agricultural activities source, dominated by Hg (73.01%); (3) atmospheric deposition sources, with Pb (85.11%) as the main contributor; (4) natural source, characterized by Cr (72.96%), Ni (66.04%), As (55.98%) and Cu (37.70%). This study would help us understand the pollution characteristics and sources of farmland soils in mining areas and provide basic information for the next step of pollution control and remediation.

Mineral phases and release behaviors of as in the process of sintering residues containing as at high temperature.

To investigate the effect of sintering temperature and sintering time on arsenic volatility and arsenic leaching in the sinter, we carried out experimental works and studied the structural changes of mineral phases and microstructure observation of the sinter at different sintering temperatures. Raw materials were shaped under the pressure of 10 MPa and sintered at 1000~1350°C for 45 min with air flow rate of 2000 mL/min. The results showed that different sintering temperatures and different sintering times had little impact on the volatilization of arsenic, and the arsenic fixed rate remained above 90%; however, both factors greatly influenced the leaching concentration of arsenic. Considering the product's environmental safety, the best sintering temperature was 1200°C and the best sintering time was 45 min. When sintering temperature was lower than 1000°C, FeAsS was oxidized into calcium, aluminum, and iron arsenide, mainly Ca3(AsO4)2 and AlAsO4, and the arsenic leaching was high. When it increased to 1200°C, arsenic was surrounded by a glass matrix and became chemically bonded inside the matrix, which lead to significantly lower arsenic leaching.

[Structural changes in mineral phases and environmental release behavior of arsenic during sintering of arsenic-containing waste].

An experimental work was carried out to investigate the effect of sintering temperature on arsenic volatility, arsenic leaching of the sinter and structural changes in mineral phases of arsenic in the sinter. The raw materials were shaped under the pressure of 10 MPa and sintered at 1 000-1 350 degrees C for 60 min with the air flow rate of 2 000 mL x min(-1). The results showed that there was little impact between the volatilization of arsenic before and after sintering, and arsenic fixed-rate remained above 90%, however, the sintering temperature had an important influence on the leaching concentration of arsenic. When sintering temperature was lower than 1 000 degrees C, FeAsS was oxidized into calcium arsenate, aluminum arsenate, and iron-arsenate. Ca3 (AsO4)2 was the main compound, and the release of arsenic leaching was high. When sintering temperature was up to 1 200 degrees C, the arsenic was surrounded by a glass matrix and became chemically bonded inside the matrix. Arsenates can be converted into silicoarsenates during sintering, which led to the leaching of arsenic was significantly lower. Considering the product's environmental safety, the best sintering temperature was 1 200 degrees C.