Journal
CHEMOSPHERE
Volume 255, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.chemosphere.2020.126036
Keywords
gypsum; alpha-calcium sulfate hemihydrate; arsenate; Sulfate; Distribution; Compatibility
Categories
Funding
- National Key Research and Development Program of China [2019YFC040880]
- NSFC [51502277]
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Transforming gypsum into alpha-calcium sulfate hemihydrate (alpha-HH) provides a promising utilization pathway for the abundant amount of chemical gypsum. The transformation follows the route of dissolution-recrystallization, during which the arsenic pollutant in gypsum is released into the solution, and hence raises the possibility of being distributed into the product of alpha-HH, a potential harm that has always been neglected. Investigation of the transformation process at neutral pH revealed that the arsenate ions in solution were distributed into alpha-HH and generated an enrichment of arsenic by 4-6 times. Arsenate ions distributed into alpha-HH by substitution for lattice sulfate, adsorption on alpha-HH facets and occupation for surface sulfate sites. While at higher concentrations, calcium arsenate coprecipitated with alpha-HH or even crystallized independently. Increasing temperature accelerated the phase transformation and restrained arsenate migration into alpha-HH due to the lag of distribution balance. The pH of solution modulated the dominant arsenate species and decreasing pH weakened arsenate substitution capacity for sulfate in alpha-HH. This work uncovers arsenate distribution mechanism during the transformation of gypsum into alpha-HH and provides a feasible method to restrain arsenate distribution into product, which helps to understand arsenate behavior in hydrothermal solution with high concentration of sulfate minerals and provides a guidance for controlling pollutants distribution into product. (C) 2020 Elsevier Ltd. All rights reserved.
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