Long-term effectiveness of lead precipitation as carbonate and its stability under acidic conditions by using activated serpentine mineral

Abstract

Utilization of readily accessible serpentine mineral, for lead removal from wastewater is a sustainable strategy, but the adsorption capacity of the raw serpentine is limited due to its small interlayer spacing and low surface reactivity, not to say the cases under acidic conditions. In this study, natural serpentine was simply ball-milled to obtain enhanced reactivity and dissolution due to the generation of various lattice defects, which allowed the highly efficient lead fixation even under acidic conditions (at initial pH of 3), compared to that driven by the surface adsorption. Characterizations demonstrated the continuous dissolution of serpentine in solution with the reaction time prolonged, inducing the heterogeneous precipitation of significant (basic) lead carbonate on serpentine surface with an aid of even very dilute atmospheric CO2, which worked as the dominated mechanism for enhancing the whole lead fixation efficiency. Results showed that more than 99.5 % of soluble lead could be immobilized within 1 ∼ 2 h with serpentine dosage of 0.5 g/L under low concentration (5 ∼ 100 mg/L), with a high lead fixation capacity about 1782.9 mg/g after 48 h under high concentration (1000 mg/L). Moreover, the stability of the Pb-bearing sediment under acidic exposure (pH 3) for 24 h was confirmed, and the dissolved lead from chloride and sulfate salts could also be immobilized using the as-proposed strategy. Altogether, these findings demonstrated the high efficiency and long-term effectiveness of lead fixation on the ball-milled serpentine, which makes it a promising candidate for application to green remediation of heavy metal contaminations in various sites along with the utilization of waste mineral resources.