Immobilization of arsenic in different contaminated soils by zero-valent iron-embedded biochar: Effect of soil characteristics and treatment conditions

Although zero-valent iron-embedded biochar (ZVI-BC) has been proposed as an effective amendment for arsenic (As)-contaminated soils, the impacts of soil characteristics and treatment conditions on the remediation process remained poorly understood. Herein, the immobilization of As in four As-contaminated soils (i.e., smelting soil, storage soil, agricultural soil, and mining soil) by ZVI-BC under different amendment dosages, cultivation temperatures, and soil moisture contents were investigated. ZVI-BC showed high As immobilization capacity in all four soils via forming the AsFe co-precipitation, and the liable As was reduced by 82.4-97.0 % with a 2 % (w/w) amendment. The higher temperature could raise the concentration of liable As in all four soils, especially for the storage soil, in which liable As at 35 °C was almost 3 times of that at 25 °C after 50-days treatment, because the elevated temperature enhanced the destruction of the generated AsFe coprecipitation as well as the desorption of As in soils. Too much soil moisture was unfavorable for the As immobilization after 50-days treatment. Flooding tended to inhibit the community diversity of As-detoxicated bacteria, e.g., Halomonas, Bryobacter, and Anaerolinea, thus resulting in the release of liable As. According to the correlation analysis, the crucial influencing factor for As immobilization was different in four soils, which was determined by the soil properties and proportion of liable As. Our study indicates that ZVI-BC is an effective amendment for As immobilization under various conditions, and the biogeochemical processes of As-associated Fe minerals determine the As immobilization during amendment.