LAUSR

Arsenic (As) contamination is a widespread problem. Continued and concerted effort in exploring sustainable remediation strategies is required, with in-situ immobilization emerging as a promising option. This work valorized a waste by-product from olive milling into functional hydrochar. The hydrochar was then transformed into iron oxide encapsulated carbon with three different iron loading rates (10%, 25%, and 50% w/w of iron chloride hexahydrate added to the olive mill waste feedstock). Both the hydrochar and the three iron oxide encapsulated carbon materials were then tested, in a pot trial using a 3% w/w application rate, as a means to immobilize As in a mining contaminated soil (2580±110 mg/kg As). After a 45-day incubation period, the effect of adding the amendments on arsenic mobility and bioaccessibility compared to an untreated control was measured using a sequential extraction procedure (SEP) and in vitro bioaccessibility (IVBA), respectively. All four treatments resulted in a decrease in mobility and in vitro bioaccessibility as compared with the control. Specifically, As in the mobile phases was up to 35% less than the in control, while bioaccesibility was 21.8% in the control and ranged from 17.5 to 12.3% in the treatments. The efficiency of amendments to immobilize As increased with the iron content of the developed materials. This work positions hydrochars and iron oxide encapsulated carbon materials produced from olive mill waste as promising options to immobilise As in-situ. This article is protected by copyright. All rights reserved.