Synergistic reduction and adsorption strategies for the efficient recovery of iodine from shale gas wastewater

A coupled redox-adsorption-desorption-precipitation process successfully recovered iodine from SGW concentrate. • After sixth adsorption cycles, the removal rate of iodine bu. PAC exceeded 79%. • Iodine with a purity of over 90% was recovered from the SGW concentrate. • The cost of treating one ton of water is only about 1 RMB, which offers significant economic value. The concentrated shale gas wastewater (SGW) contains high concentrations of iodine, presenting challenges for efficient recovery. This work reports the successful recovery of iodine from SGW concentrate using a combination of redox, adsorption, desorption, and precipitation processes. The process starts with ozone (O 3 ) pre-oxidation, converting iodide ions (I − ) into iodate ions (IO 3 − ). After comparing the performance of the six reducing agents, it was found that a 90% removal rate of iodine in the SGW concentrate could be achieved by first carrying out a ferrous ion reduction reaction, followed by adsorption using powdered activated carbon (PAC) for one day. Upon a series of process optimizations, an 83.8% removal rate of iodine from the SGW concentrate was achieved when 0.19 g/L ferrous sulfate and 0.35 g/L PAC were present simultaneously for 20 min. This results from the synergistic action of ferrous ions reduced by I − while PAC rapidly adsorbing I 2 . The PAC adsorption capacity remained at 71.1 mg/g, with an iodine removal rate exceeding 79.1% and a desorption rate of 89.5%, after six adsorption and desorption cycles. Lastly, by subjecting the PAC desorption solution to alkali washing and oxidation, the I 2 was successfully recovered with a purity of 99%. This integrated approach offers a promising strategy for the purification and recovery of iodine resource from SGW concentrate. Download: Download high-res image (172KB) Download: Download full-size image