Field demonstration of on-site immobilization of arsenic and lead in soil using a ternary amending agent

Soil contamination by heavy metals and metalloids has been a major environmental challenge. While various remediation technologies have been reported, field data on the remediation effectiveness have been limited. We tested a new remediation technology for on-site immobilization of As(III) and Pb(II) in a contaminated soil at an abandoned chemical plant site. A novel ternary amending agent consisting of Fe 2 O 3 , MnO 2 , and Mg(OH) 2 (molar ratio = 1.0:5.5:5.5) was used to amend the soil on-site . Field monitoring data indicated that the amendment severed as a pH buffer and a long-term sequester for both As and Pb in the soil. At a dosage of 3 wt%, the acid-leachable As and Pb were lowered from 0.042–0.077 mg/L and 0.013–0.022 mg/L to 0.0062–0.0093 mg/L and 0.0030–0.0080 mg/L, respectively, after one day of the amendment, and to 0.0020–0.0050 mg/L and 0.0020–0.0054 mg/L after 240 days of aging. As(III) was oxidized to As(V) and subsequently immobilized via complexation and precipitation, whereas Pb(II) was sequestered via electrostatic attraction and chemical precipitation . The treatment cost was estimated at $31.5/m 3 . The results indicate that complex contaminants in soil can be effectively immobilized using combined amending agents that can interact with the target chemicals and induce synergistic immobilization reactions.