Electroplating wastewater treatment process and ion exchange treatment method (3)?

Membrane separation technology

Membrane separation is a technology that uses the selectivity of polymers to separate substances, including electrodialysis, reverse osmosis, membrane extraction, ultrafiltration, etc. Electrodialysis is used to treat electroplating industrial wastewater, and the composition of the wastewater remains unchanged after treatment, which is conducive to returning to the tank. Wastewater containing Cu2+, Ni2+, Zn2+, Cr6+ and other metal ions is suitable for electrodialysis treatment, and there are complete sets of equipment. The reverse osmosis method has been used on a large scale for the treatment of Zn, Ni, Cr rinsing water and mixed heavy metal wastewater. Reverse osmosis is used to treat electroplating wastewater, and the treated water can be reused to realize a closed loop. There are many research reports on the treatment of electroplating wastewater by liquid membrane method. In some fields, the liquid membrane method has entered the preliminary industrial application stage from basic theoretical research. Liquid processing [7]. Membrane extraction technology is an efficient, no secondary pollution separation technology, this technology has made great progress in metal extraction.

Ion exchange treatment method

The ion exchange treatment method is a method of separating harmful substances in wastewater by using ion exchangers. The ion exchangers used include ion exchange resins, zeolites, etc., and ion exchange resins include gel type and macroporous type. The former is selective, and the latter is complicated to manufacture, costly, and consumes a large amount of regenerant, so its application is greatly restricted. Ion exchange is achieved by ion exchange between the freely movable ions carried by the exchanger itself and the ions in the solution being treated. The driving force for ion exchange is the concentration difference between ions and the affinity of the functional groups on the exchanger to ions. In most cases, ions are first adsorbed and then exchanged. Ion exchangers have dual functions of adsorption and exchange. The application of this material is increasing, such as bentonite [11], which is a clay with montmorillonite as the main component, which has good water swellability, large specific surface area, strong adsorption capacity and ion exchange capacity. After the improvement, its adsorption and ion exchange ability is stronger. However, it is more difficult to regenerate. Natural zeolite has greater advantages than bentonite in the treatment of heavy metal wastewater: Zeolite [9] is an aluminosilicate mineral with a grid structure, which is porous in the interior and has a large specific surface area. Absorption and ion exchange capacity. Studies have shown [10] that the mechanism by which zeolite removes heavy metal ions from wastewater in most cases is the dual role of adsorption and ion exchange. As the flow rate increases, ion exchange will take the lead in replacing adsorption. If the natural zeolite is pretreated with NaCl, the adsorption and ion exchange capacity can be improved. Through the process of adsorption and ion exchange regeneration, the concentration of heavy metal ions in the wastewater can be concentrated and increased by 30 times. Zeolite removes copper. During the NaCl regeneration process, the removal rate is more than 97%, and it can be adsorbed and exchanged for multiple times, and regeneration cycles, and the removal rate of copper is not reduced.

Biological treatment technology

Biological flocculation is a decontamination method that uses microorganisms or metabolites produced by microorganisms for flocculation and sedimentation. Microbial flocculants are metabolites that are produced by microorganisms and secreted out of the cell with flocculating activity. Generally, it is composed of polysaccharides, proteins, DNA, cellulose, glycoproteins, polyamino acids and other high-molecular substances. The molecules contain a variety of functional groups that can cause colloidal suspensions in water to cohere and precipitate each other. Up to now, there are about a dozen varieties of heavy metals that have a flocculating effect. The amino and hydroxyl groups in biological flocculants can form stable chelate complexes with heavy metal ions such as Cu2+, Hg2+, Ag+, and Au2+ to precipitate. The application of microbial flocculation method to treat wastewater is safe, convenient, non-toxic, does not produce secondary pollution, has good flocculation effect, fast growth, and easy to realize industrialization. In addition, microorganisms can be genetically engineered, domesticated or constructed into strains with special functions. Therefore, the microbial flocculation method has broad application prospects.

Biological flocculation method

The adsorption method is an effective method to remove heavy metal ions by using the unique structure of the adsorbent. The adsorbents used to treat electroplating heavy metal wastewater by adsorption method include activated carbon, humic acid, sepiolite, polysaccharide resin and so on. Activated carbon is simple in equipment and widely used in wastewater treatment. However, the regeneration efficiency of activated carbon is low, and the treated water quality is difficult to meet the reuse requirements. It is generally used for the pretreatment of electroplating wastewater. Humic acid substances are relatively inexpensive adsorbents, and humic acid is made into humic acid resin to treat Cr-containing and Ni-containing wastewater with successful experience. Related studies have shown that chitosan and its derivatives are good adsorbents for heavy metal ions. After the chitosan resin is cross-linked, it can be reused 10 times without significant reduction in adsorption capacity [5]. Using modified sepiolite to treat heavy metal wastewater has a good adsorption capacity for Pb2+, Hg2+, and Cd2+, and the heavy metal content in the treated wastewater is significantly lower than the comprehensive sewage discharge standard. It is also reported in the literature that montmorillonite is also a good clay mineral adsorbent. The removal rate of Cr 6+ by aluminum-zirconium pillared montmorillonite under acidic conditions is 99%, and the Cr 6+ content in the effluent is lower than the national emission. Standard, with practical application before heat [6].

Biosorption method

The biosorption method is a method that uses the chemical structure and composition characteristics of the organism to adsorb metal ions dissolved in water, and then removes the metal ions in the aqueous solution through solid-liquid two-phase separation. Using extracellular polymers to separate metal ions, some of the proteins released by bacteria during the growth process can convert soluble heavy metal ions in the solution into precipitates and remove them. Biosorbent has the characteristics of wide sources, low price, strong adsorption capacity, easy separation and recovery of heavy metals, etc., and has been widely used.

Biochemical method

Biochemical method refers to the treatment of heavy metal-containing wastewater by microorganisms to convert soluble ions into insoluble compounds and remove them. The sulfate biological reduction method is a typical biochemical method. In this method, under anaerobic conditions, sulfate-reducing bacteria reduce sulfate to H2S through dissimilative sulfate reduction. The heavy metal ions in the wastewater can react with the generated H2S to form metal sulfide precipitation with very low solubility. At the same time, the reduction of H2SO4 can convert SO42- into S2- and increase the pH value of wastewater. Because many heavy metal ion hydroxides have a small ion product, they precipitate. Relevant studies have shown that the removal rate of wastewater containing Cr 6+ with a concentration of 30-40 mg/L by biochemical methods can reach 99.67%-99.97% [11]. Someone also used livestock manure anaerobic digestion sludge for the treatment of heavy metal ions in mine acid wastewater, and the results showed that this method can effectively remove heavy metals in wastewater. Zhao Xiaohong et al. [12] used Enterobacter desulfurization (SRV) to remove copper ions in electroplating wastewater. In a solution with a copper mass concentration of 246.8 mg/L, when the pH was 4.0, the removal rate reached 99.12%.

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