Friedel's Salts Synthesis and Adsorption Applications in the Removal of As(III) and Se(IV) from Desulfurization Wastewater

Coal-fired power plants are one of the major sources of arsenic and selenium emissions. So far, the use of the traditional triple tank process for treating desulfurization wastewater containing arsenic and selenium has not met the demand for zero emissions from power plants, and the direct introduction of layer double hydroxides (LDHs), a new class of inorganic functional material with a high-efficiency adsorption capacity, would result in secondary pollution and resource waste. Here, we found that the calcium oxide component used in the conventional process, in the presence of sodium meta-aluminate and chlorine, generates Friedel's salts with LDHs. Based on this mechanism, we developed a method to prepare LDHs using desulfurization solid waste and reused it for the adsorption of arsenic and selenium, obtaining adsorption efficiencies of up to 86.34 and 92.74%, respectively, with maximum adsorption capacities of 0.7365 and 0.8864 mg/g at a dosage of 2.4 g/L and a temperature of 70 degrees C. The adsorption process was identified as monolayer chemisorption, and the adsorption kinetics and isotherms could be described by pseudo-second-order and Langmuir models. The practical application of the adsorbent was demonstrated by investigating the competitive and synergistic adsorption mechanisms of multiple heavy metals, showing that the method can be an industrial tool for the secondary use of desulfurization waste and the efficient removal of heavy metals such as arsenic and selenium. This is a breakthrough in achieving the goal of zero emissions from coal-fired power plants.