Temperature effects on Cu2+ removal from synthetic wastewater using alumina-rich refining slag: Performance and mechanism

Abstract

In this study, the influence of temperature on Cu²⁺ removal efficiency by alumina(Al)-rich refining slag (RS) from synthetic wastewater prepared using CuSO₄ was investigated and the removal mechanisms at different temperatures were elucidated. Batch experiments conducted at 20–80 °C revealed that elevated temperatures significantly enhanced Cu²⁺ removal efficiency, with optimal dosage requirements decreasing dramatically from 13-19 g/L at 20 °C to 0.2–0.4 g/L at 80 °C for achieving >99 % removal efficiency within 15 min. The enhanced performance was attributed to the accelerated hydration of Ca₁₂Al₁₄O₃₃ in RS. This process increased the solution alkalinity and promoted the formation of CuCaAl-layered double hydroxide (LDH) through co-precipitation with Ca²⁺ and Al(OH)₄^- ions, wherein SO₄²⁻/CO₃²⁻ anions were intercalated. At 20 °C, CuCaAl-LDH was less likely to be generated and Cu(OH)₂ precipitation was a primary Cu²⁺ removal route. Concurrently, hydrolysis of CaS in RS released S²⁻ ions, enabling temperature-independent CuS precipitation across all tested temperatures. These findings highlighted Al-rich RS as a low-cost precipitant for efficient Cu²⁺ sequestration, with optimal performance achieved at 60–80 °C. Moreover, the in-situ formed LDH phases, acting as an excellent adsorbent, rendered the Cu²⁺-treated RS a potential multifunctional material for wastewater remediation.