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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.

A phytoextraction experiment with five Cd hyperaccumulators (Amaranthus hypochondriacus, Celosia argentea, Solanum nigrum, Phytolacca acinosa and Sedum plumbizincicola) was conducted in two soils with different soil pH (5.93 and 7.43, respectively). Most accumulator plants grew better in the acidic soil, with 19.59–39.63% higher biomass than in the alkaline soil, except for S. plumbizincicola. The potential for a metal-contaminated soil to be cleaned up using phytoremediation is determined by the metal uptake capacity of hyperaccumulator, soil properties, and mutual fitness of plant-soil relationships. In the acidic soil, C. argentea and A. hypochondriacus extracted the highest amount of Cd (1.03 mg pot−1 and 0.92 mg pot−1, respectively). In the alkaline soil, S. plumbizincicola performed best, mainly as a result of high Cd accumulation in plant tissue (541.36 mg kg−1). Most plants achieved leaf Cd bioconcentration factor (BCF) of >10 in the acidic soil, compared to

Transformation of soil Pb to pyromorphites and phosphates has the potential to be an effective strategy to immobilize this contaminant in situ. Soil treatment using monocalcium phosphate, a commercial fertilizer (NTS Soft Rock) and biochars prepared from poultry litter and from biosolids at three different temperatures (300, 400, and 500°C) and two doses (1 and 3%) were evaluated. Lead bioaccesibility, mobility, and solid speciation were measured. Leachable Pb (determined with the toxicity characterized leaching procedure) was not significantly ( > 0.05) changed after biochar addition, but a significant decrease in bioaccesible Pb was found for several treatments ( < 0.05). This was particularly notable for treatments receiving biosolids prepared at 400 and at 500°C or monocalcium phosphate at the 3% dose. The decrease in bioaccesible Pb concentration in the biochar treatments was similar to traditional phosphate amendments. Our research found transformation of Pb species to the more stable pyromorphite and Pb-phosphate to be partially responsible for the observed changes, although other mechanisms, including pH changes, might also play an important role. Overall, pyrolysis was an effective method to upgrade waste streams and facilitate Pb immobilization, although key pyrolysis parameters need to be selected carefully.