Enhanced Arsenic Removal from Nickel Sulfate Solutions Through Heteropoly Acid Formation

Arsenic is a highly toxic contaminant commonly found in various non-ferrous metal ores, spreading through multiple stages of the smelting process and creating significant environmental and production problems. In nickel metallurgy, high arsenic levels in nickel sulfate solutions not only severely lower the quality of electrolytic nickel but also lead to hazardous waste disposal issues. In acidic nickel sulfate solutions, trace arsenic mainly exists as H 3 AsO 4 , which is difficult to remove with standard anion- or cation-exchange resins. In this study, a new approach was developed by adding sodium tungstate to nickel sulfate solutions at a molar ratio of n (As): n (W) = 1:12 to facilitate binding with H 3 AsO 4 , thereby forming stable arsenic–tungsten heteropoly acid (HPA) clusters and enhancing the adsorption performance of the D301 ion-exchange resin. The arsenic–tungsten HPA-loaded resin was then eluted using sodium hydroxide (NaOH) solution. Under optimized conditions (pH 1.5, 60 °C), this process lowered arsenic levels from 55.45 mg/L to less than 1 mg/L, meeting industrial standards. The desorption efficiency for both arsenic and tungsten was over 97 pct, with a molar ratio n (As): n (W) around 1:12 in the eluate, confirming the stability of the HPA structure. This research provides a reliable technical method for deep arsenic removal and offers a practical solution for arsenic contamination in non-ferrous metal smelting processes.