Treatment of Mercury Refine Effluents
Mercury is one of the major hazardous substances generated during the refining process. Mercury (Hg) is known to be toxic and has been classified as a potent environmental pollutant. It is released as contamination into water sources with potentially damaging effects for aquatic life and human health. The mercury compounds are compounds formed when mercury is oxidized. These compounds have a wide range of toxicity, depending on the type of mercury compound.
For industrial plants using mercury-containing processes, the release of mercury to the environment can be prevented through an effective mercury control program which includes monitoring, sampling, and treatment. The mercury treatment system should be based on the type, concentration, form and chemical composition of mercury waste effluents as well as the effluents intended method of disposal.
The typical methods of mercury removal from effluents include precipitation, chemical reduction, ion exchange, and adsorption. Precipitation involves adding chemicals that form insoluble compounds with mercury and cause it to settle out of the wastewater stream. Chemical reduction involves adding reducing agents to convert mercury to its least toxic states, usually elemental or metallic mercury. Thereafter, the elemental mercury can be isolated and removed by sedimentation or destratification or filtration or differential centrifugation.
Ion exchange is based on the chemical principle that a charged ion can be removed from solution by an exchange with another charged ion. The ion exchange resins carry two types of functional groups, one having a positive charge to attract negatively charged ions and another that has a negative charge to adsorb positively charged ions like mercury. Adsorption is the process of attaching fine particles of the pollutant onto the surface of a raw material, such as carbon and is particularly effective for removing metals from wastewater such as mercury.
In addition to traditional chemical treatments for mercury removal, modern technology also includes membrane-based technologies, such as reverse osmosis (RO), nanofiltration (NF) and ultrafiltration (UF). Reverse osmosis requires a relatively high pressure when compared to other membrane-based technologies and is particularly effective for removing high concentrations of salts and heavy metals such as mercury.
The overall treatment process depends on several factors such as the type of wastewater, the conditions of the wastewater environment, wastewater treatment methods, the degree of removal required and the chemical composition of the effluent. A full-scale treatment system should be designed based on these factors. In conclusion, depending on the type and concentration of mercury in the waste effluent, there are various treatment methods available to treat mercury effluent. All of these treatments can help to reduce the environmental impacts associated with a discharge of mercury-containing effluents.
