Simultaneous arsenate and alkali removal from alkaline wastewater by in-situ formation of Zn–Al layered double hydroxide

Abstract

An effective and facile method was developed to remove As(V) and alkali simultaneously from alkaline wastewater based on the repeated in-situ formation of Zn–Al–AsO4 layered double hydroxide (ZnAl–AsO4 LDH). The removal efficiency of As(V) was almost 100% and the pH of the treated alkaline wastewater decreased from 12 to 7.47. Removal of As(V) was not affected by competitive anions such as SO42−, F−, Cl−, and NO3− due to the large binding energy between As(V) and LDH sheets as confirmed by calculations based on the Castep Module of Materials. About 96% of As(V) can be released and concentrated into a small volume of Na2CO3 solution for disposal or recovery. The LDH was then dissolved in HNO3 and the solution can be used to treat wastewater to reform Zn–Al LDH for further removal of arsenate. This process was repeated four times but after the fifth cycle, the removal efficiency went down by the loss of Al3+ to solution but the process can be repeated by replenishing the solution with Al3+. The newly developed process is eminently suited for remediation of arsenate and alkali simultaneously from alkaline wastewater.