Gel plating-Research Progress of Electroplating Wastewater treatment Technology in China

Gel plating-Research Progress of Electroplating Wastewater treatment Technology in China.
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Electroplating is widely used in automobile, electronic and electrical appliances, aerospace industry, construction industry and corresponding decoration industry. The discharge of electroplating wastewater corresponding to the scale development of electroplating industry is also increasing, and electroplating has become one of the most serious polluting industries in the world. At present, there are about 15000 electroplating factories in China, and about 50% of the 4 billion m ~ 3 wastewater discharged each year does not meet the national discharge standards. these wastewater contain cyanide, acid, alkali, hexavalent chromium, copper, zinc, cadmium, nickel and other heavy metal pollutants. very toxic, serious harm. Therefore, the treatment of electroplating wastewater is still a problem that can not be ignored. The common treatment methods of electroplating wastewater include chemical precipitation, ferrite, ion exchange, membrane separation and so on. This paper mainly introduces the application and research progress of the above methods in electroplating wastewater, and makes some comments on them, in order to provide some theoretical reference for the treatment of electroplating wastewater in our country.
1 chemical precipitation method.
Chemical precipitation methods include hydroxide precipitation, sulfide precipitation and sulfuric acid double salt precipitation. It is a process in which the pH range of heavy metal ions is calculated according to their different solubility products and initial concentrations, and then precipitated completely at a certain pH value by adding precipitants.
SNHosseini and others use alkaline reagents such as lime and sodium hydroxide to treat the wastewater containing copper and chromium. When the pH is 12 and 8.7 respectively, Cu2+ and Cr3+ are completely precipitated, and the wastewater can meet the discharge standard. HamidiAAziz and others use limestone to treat wastewater containing heavy metals, and adjust the terminal pH value to 8.5 with a certain amount of limestone, and the removal rate of heavy metal ions can reach more than 90%. Yin Jingqun and others carried out gypsum-vulcanization treatment of the acidic wastewater containing heavy metals, fluorine, arsenic and other toxic and harmful elements in a copper smelter, and further neutralized it with lime milk, and the wastewater reached the national first-class discharge standard.
2 ion exchange method.
The ion exchange method mainly uses the exchange ions in the ion exchange resin to exchange with some ions in the electroplating wastewater to remove them and purify the wastewater. In recent years, this technology has made great progress in wastewater treatment, and has become one of the effective means to treat electroplating wastewater and recover some metal ions.
Rengaraj et al studied the removal rate of Cr (III) by IRN77 and SKN1 resin. The results show that when the concentration of metal ions is higher than that of 100mg/L, it can be completely adsorbed by the resin. RSJuang et al used strong acid AmberliteIR-120 resin to treat mixed wastewater containing many kinds of heavy metal ions [(Ni (II), Mn (II) and Co (II)] and ED-TA, NTA and citrate. It was found that the exchange balance of metal ions and resin mainly depended on the composition of pH and other complex components in the wastewater. THEom et al use ion exchange method to treat electroplating wastewater, and the metal recovery rate is more than 97%. SofiaAC et al tested chelating resin CR11 and weakly acidic resin IR86. The results show that both resins have high adsorption of trivalent chromium in aqueous solution, and CR11 resin is more promising than IRC86 resin in the treatment of electroplating wastewater. RSJuang et al studied the adsorption of nickel in simulated electroplating wastewater with strong acid resin. The results show that with the increase of time, the content of nickel in the wastewater becomes less and less, but due to the existence of other impurities in the wastewater, the discharge of nickel can not be zero.
3 adsorption method.
Adsorption has become an untraditional method for the treatment of electroplating wastewater, which is a water treatment process of adsorption and separation of pollutants from water by porous solid phase. A variety of low-cost adsorbents produced from agricultural wastes, industrial by-products, natural materials and modified biopolymers have been developed and applied, such as activated carbon, activated coal, coke, cinder, resin, sawdust and so on.
The magnetic zeolites synthesized by Nah and others modified by iron oxide have high adsorption capacity for Pb (II) and good chemical impedance in a wide pH range (5-11). Aklil and other modified natural materials were used for adsorption in pH=5, and good adsorption results were obtained. Lee uses industrial by-products such as fly ash, scrap iron, iron slag and hydrated titanium dioxide to adsorb heavy metal wastewater with high removal rate.
4 membrane filtration method.
The membrane separation process is a process in which the substance passes through or is intercepted in the membrane, which is similar to the screening process. According to the size of separated ions, it can be divided into microfiltration, ultrafiltration, reverse osmosis, nanofiltration and so on. The membrane separation method has the advantages of no phase change, high energy conversion efficiency, no consumption of chemical reagents, normal temperature operation, no heat consumption and so on.
Juang and Shiau studied the removal of Cu (II) and Zn (II) from simulated wastewater by chitosan modified membrane. The results showed that 100% of Cu (II) and 95% of Zn (II) were intercepted at pH8.5~9.5. Saffaj and others use low-cost ZnAl2O4-TiO2UF membrane to adsorb Cd (II) and Cr (III) in the simulated solution, and the removal rate of Cd (II) reaches 93%. The removal rate of III reaches 86%. Lv et al have studied the removal of anions and cations by amphoteric polybenzimidazole nanohollow fiber membranes, and more than 90% of the dissolved matter can be blocked.