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

Abstract

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•Cr₂H₂(SO₄)₄•2H₂O, Cr(OH)₃•3H₂O, Cu(OH)₂•2H₂O and 3Cu(OH)₂•CuSO₄•2H₂O] 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•1•7 phases changed with varying amounts of copper and chromium ions. It was confirmed that copper and chromium ions entered the 5•1•7 phase crystal structure by atom substitution.