In situ stabilization of arsenic in soil with organoclay, organozeolite, birnessite, goethite and lanthanum-doped magnetic biochar

Abstract

Arsenic (As) is a known carcinogen and naturally occurring semi-metal in soils and in the Earth's crust. Contamination of soils and water with As poses a serious threat to millions of people worldwide due to its health hazards and toxicological properties. Hence, devising novel and efficient methods for remediation of contaminated areas has attracted a great deal of interest across the globe. In this study, we investigated the usefulness of synthetic birnessite, goethite, hexadecylpyridinium chloride-modified montmorillonite (HDPC-M), hexadecylpyridinium bromide-modified zeolite (HDPB-Z), and lanthanum (La)-doped magnetic biochar produced from eucalyptus bark (La-Euchar) as adsorbents at 10% dosage for As stabilization in a soil spiked with 1 000 mg kg-1 As. The effectiveness of the above adsorbents in As immobilization in soil was assessed using single-step extractions with 2 mol L-1 HNO3 and deionized water, the simplified bioaccessibility extraction test (SBET) method, and sequential extraction with the modified Community Bureau of Reference (BCR) method. Application of the adsorbents shifted the exchangeable fraction of As to more recalcitrant fractions and dramatically reduced the exchangeable fraction by 6%–99% and the extractable amounts with HNO3, deionized water, and SBET method by 30%–92%, 17%–95%, and 12%–90%, respectively, compared to the unamended control. The immobilizing effects of adsorbents on As decreased in the sequence of birnessite >La-Euchar >goethite >HDPB-Z >HDPC-M. Birnessite exhibited great affinity for As and drastically reduced As extractability by more than 90% in all single extractions. The results revealed that HDPC-M, HDPB-Z, La-Euchar, birnessite, and goethite are promising immobilizing agents for in situ stabilization of As in terrestrial environments.