Study on the Mechanical Properties and Leaching Mechanism of Cr3+ and Cu2+ Cured by Basic Magnesium Sulfate Cement

Cr3+ and Cu2+ can be cured using basic magnesium sulfate cement (BMSC). The influence of compressive strength, water resistance, and leaching characteristics of BMSC-solidified bodies was studied to evaluate the applicability of BMSC cement in industrial solid waste treatment. XRD, SEM, MIP, TG and FTIR were used to analyze the hydration products and microstructures of the solidified BMSC. The results show that when the content of Cr3+ or Cu2+ accounts for 0.2% to 2% of the molar mass of MgO, the addition of Cr3+ and Cu2+ inhibits the hydration reaction of BMSC, which causes the compressive strength to decrease, but the lowest strength is still have 27.6 MPa. The Cr3+ or Cu2+ BMSC-solidified body has good water resistance. The highest leaching concentrations in the solidified product are just 0.221 mg/L and 0.508 mg/L. XRD and microscopic analyses show that four new phases [4Cr(OH)(3)center dot Cr2H2(SO4)(4)center dot 2H(2)O, Cr(OH)(3)center dot 3H(2)O, Cu(OH)(2)center dot 2H(2)O and 3Cu(OH)(2)center dot CuSO4 center dot 2H(2)O] are formed after adding Cr3+ and Cu2+, which shows that BMSC cement can cure heavy metals through chemical reactions. During the solidification process, the interplanar spacing of the 5 center dot 1 center dot 7 phases changed with varying amounts of copper and chromium ions. It was confirmed that copper and chromium ions entered the 5 center dot 1 center dot 7 phase crystal structure by atom substitution.