The composition of electroplating wastewater is very complex. In addition to cyanide containing (CN -) wastewater and acid-base wastewater, heavy metal wastewater is a potentially hazardous category of wastewater in the electroplating industry. According to the classification of heavy metal elements contained in heavy metal wastewater, it can generally be divided into wastewater containing chromium (Cr), nickel (Ni), cadmium (Cd), copper (Cu), zinc (Zn), gold (Au), and silver (Ag).

Adsorption is a useful method for removing heavy metal ions by utilizing the common structure of adsorbents. The adsorbents used for treating electroplating heavy metal wastewater by adsorption method include activated carbon, humic acid, sepiolite, and polysaccharide resin. Activated carbon equipment is simple and widely used in wastewater management, but the regeneration efficiency of activated carbon is low, and it is difficult to meet the reuse requirements for water treatment. It is generally used for pre-treatment of electroplating wastewater.

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Using modified sepiolite to manage heavy metal wastewater for Pb2 Hg2 and Cd2 have good adsorption capacity, and the heavy metal content in the treated wastewater is significantly lower than the comprehensive sewage discharge standards. There are also literature reports that montmorillonite is also an outstanding clay mineral adsorbent. Aluminum zirconium pillared montmorillonite has a removal rate of 99% for Cr6 under acidic conditions, and the content of Cr6 in the effluent is lower than the emission standards, which has practical applications.

The method of participating in sulfide deposition agents to generate heavy metal ions in wastewater and remove sulfide deposits. Compared with the neutralization deposition method, the advantage of the sulfide deposition method is that the solubility of heavy metal sulfides is lower than that of their hydroxides, and the pH value of the reaction is between 7-9. The treated wastewater generally does not need to be neutralized. The drawback of sulfide deposition method is that sulfide sediment particles are small and easy to form colloids; Sulfide sedimentary agents themselves remain in water and generate hydrogen sulfide gas when exposed to acid, resulting in secondary pollution.

In order to avoid secondary pollution, British scholars have developed an improved sulfide deposition method, which selectively participates in sulfide ions and another heavy metal ion in the wastewater to be treated (the equilibrium concentration of sulfide ions in this heavy metal is higher than the equilibrium concentration of sulfides in the heavy metal pollutant to be removed). Because the sulfides of added heavy metals are more soluble than those of heavy metals in wastewater, the existing heavy metal ions in wastewater are separated first, avoiding the generation of harmful gases such as hydrogen sulfide and residual sulfide ions.

Cr in electroplating wastewater mainly exists in the form of Cr6 ions. Therefore, reducing agents are added to the wastewater to reduce Cr6 to slightly toxic Cr3 , and lime or NaOH is added to produce Cr (OH) 3 for sedimentation, separation, and removal. Chemical reduction method is one of the early management techniques for electroplating wastewater, which is widely used in China. Its management principle is simple, operation is easy to grasp, and it can withstand the impact of large amounts and high concentrations of wastewater. According to the different addition of reducing agents, it can be divided into FeSO4 method NaHSO3 method, iron filings method SO2 method, etc.

The article originates from a deodorant manufacturer http://www.scneng.com.hk