Combined Two‐Stage Xanthate Processes for the Treatment of Copper‐Containing Wastewater

Heavy metal removal is mainly conducted by adjusting the wastewater pH to form metal hydroxide precipitates. However, in recent years, the xanthate process with a high metal removal efficiency, attracted attention due to its use of sorption/desorption of heavy metals from aqueous solutions. In this study, two kinds of agricultural xanthates, insoluble peanut‐shell xanthate (IPX) and insoluble starch xanthate (ISX), were used as sorbents to treat the copper‐containing wastewater (Cu concentration from 50 to 1,000 mg/L). The experimental results showed that the maximum Cu removal efficiency by IPX was 93.5 % in the case of high Cu concentrations, whereby 81.1 % of copper could rapidly be removed within one minute. Moreover, copper‐containing wastewater could also be treated by ISX over a wide range (50 to 1,000 mg/L) to a level that meets the Taiwan EPA's effluent regulations (3 mg/L) within 20 minutes. Whereas IPX had a maximum binding capacity for copper of 185 mg/g IPX, the capacity for ISX was 120 mg/g ISX. IPX is cheaper than ISX, and has the benefits of a rapid reaction and a high copper binding capacity, however, it exhibits a lower copper removal efficiency. A sequential IPX and ISX treatment (i.e., two‐stage xanthate processes) could therefore be an excellent alternative. The results obtained using the two‐stage xanthate process revealed an effective copper treatment. The effluent (C_e) was below 0.6 mg/L, compared to the influent (C₀) of 1,001 mg/L at pH = 4 and a dilution rate of 0.6 h^–1. Furthermore, the Cu‐ISX complex formed could meet the Taiwan TCLP regulations, and be classified as non‐hazardous waste. The xanthatilization of agricultural wastes offers a comprehensive strategy for solving both agricultural waste disposal and metal‐containing wastewater treatment problems.