Low-cost lanthanides and metalloid removal: Implications on arsenic mobility and bioaccessibility

This study investigates the leachability and stability of synthetic lanthanide arsenates using standardized environmental testing procedures. Lanthanum and cerium arsenates, in hydrate and anhydrous forms, were subjected to Toxicity Characteristic Leaching (TCLP) and Synthetic Precipitation Leaching (SPLP) test Procedures to evaluate arsenic mobility and stability under different environmental conditions. The results demonstrate significantly higher arsenic leachability from the hydrate phases, associated with a large specific surface area (SSA), which decreases upon calcination. LaAsO 4 ·H 2 O released approximately twice as much arsenic compared to CeAsO 4 ·1.1 H 2 O, and calcination of the hydrate phases increases the stability of the lanthanide arsenate phases. The stability findings are contextualized considering established arsenic immobilization methods. A three-category classification system for arsenic treatment methods based on their stability characteristics is proposed. Furthermore, in vitro gastro bioaccessibility (IVBA) testing revealed that the heat treatment and washing processes substantially reduced the bioaccessibility of arsenic from the lanthanide arsenates. Cerium arsenate shows promising bioaccessibility performance, with a 100-fold reduction (0.1 % As IVBA) after treatment. A preliminary treatment cost using the lanthanides with iron methods was conducted. The differences in the precipitation conditions and reagent characteristics demonstrated a reduction of 10 times the associated cost when lanthanides are used. • First assessment of lanthanides arsenate leachability and environmental testing. • Higher performance for Ce(III)-arsenate, releasing half arsenic of La(III)-arsenate. • Three-Category classification system for arsenic treatment based on leachability. • Ce(III) can surpass conventional arsenic immobilization methods.