The treatment and reuse of electroplating wastewater play a vital role in saving water resources and protecting the environment. This article reviews the advantages and disadvantages of various electroplating wastewater treatment technologies, and the application of some new materials in electroplating wastewater treatment
01 Chemical precipitation method
The chemical precipitation method is to convert the dissolved heavy metals into water-insoluble compounds by adding chemicals into the wastewater, and then separate them from the water, so as to achieve the purpose of removing heavy metals.
The chemical precipitation method is widely used in electroplating wastewater treatment because of its simple operation, mature technology, low cost, and the ability to remove multiple heavy metals in wastewater at the same time.
1. Alkaline precipitation method
The alkaline precipitation method is to add alkaline substances such as NaOH, lime, and sodium carbonate to the wastewater, so that heavy metals form hydroxides or carbonates with less solubility to precipitate and be removed. This method has the advantages of low cost and simple operation, and is currently widely used.
However, the production of sludge in the alkaline precipitation method is large, which will cause secondary pollution, and the pH of the effluent is high, and the pH needs to be adjusted. NaOH is widely used in engineering due to the relatively small amount of sludge produced and easy to recycle.
2. Sulfide precipitation method
The sulfide precipitation method is to add sulfide (such as Na2S, NariS, etc.) to make the heavy metals in the wastewater form a precipitate with a smaller solubility product than hydroxide. The pH of the effluent is 7-9, and it can be discharged without adjusting the pH.
However, the sulfide precipitation particles are small, and flocculants need to be added to assist precipitation, which increases the processing cost. Sulfide will also produce toxic HS gas in acid solution, which has limitations in actual operation.
3. Ferrite method
The ferrite method is developed based on the principle of ferrite production, which allows various heavy metal ions in the wastewater to form ferrite crystals and precipitate together, thereby purifying the wastewater. This method is mainly through adding ferrous sulfate to wastewater, after reduction, precipitation and flocculation, ferrite is finally formed. It is widely used because of its simple equipment, low cost, fast sedimentation, and good treatment effect.
The influence of pH and ferrous sulfate dosage on the removal of heavy metal ions by ferrite method. It is determined that the good flocculation pHs of nickel, zinc and copper ions are 8.00-9.80, 8.00-10.50 and 10.00, respectively. Their molar ratios are both 2-8, and the good reduction pH of hexavalent chromium is 4.00-5.50, the good flocculation pH is 8.00-10.50, and the good feed ratio is 20. The nickel content of the effluent is less than 0.5mg/L, the total chromium content is less than 1.0mg/L, the zinc content is less than 1.0mg/L, and the copper content is less than 0.5mg/L, meeting the "Emission Standard for Electroplating Pollutants" (GB21900-2008)