Chloride removal from flue gas desulfurization wastewater through Friedel's salt precipitation method: A review

As a high efficiency method for chloride removal, Friedel's salt precipitation (FSP) method has attracted much attention in zero liquid discharge (ZLD) of flue gas desulfurization (FGD) wastewater. This review provides comprehensive knowledge of FSP method for chloride removal through analysis of the evolution, reaction mechanisms and influential factors, and describes the recent research progress. FSP method is a cost-efficient technology to remove chloride from saline wastewater by adding lime and aluminate. Chloride ions react with the precipitants by adsorption or/and ion exchange to form Friedel's salt, which is affected by the reaction conditions including reaction time, temperature, interferential ions, etc. The effluent of this process can be reused as the makeup water of desulfurization tower, and the dechloridation precipitates can be reclaimed as adsorption materials and sludge conditioners. That can not only offset a fraction of the treatment cost, but also avoid secondary pollution, so ZLD of FGD wastewater can be achieved. This paper summarizes the deficiencies and potential improvement measures of FSP method. We believe this technology is a promising way to achieve ZLD of FGD wastewater and other wastewater containing chloride, and expect FSP method would become more mature and be widely applied in hypersaline wastewater treatment in the foreseeable future.