Several treatment methods for excessive heavy metals in sewage stations

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The pollution of heavy metals mainly comes from industrial pollution, followed by traffic pollution and household waste pollution. Industrial pollution is mostly discharged into the environment through waste residue, wastewater, and exhaust gas, which accumulate in humans, animals, and plants, causing great harm to the environment and human health. The treatment of industrial pollution can be reduced through some technical methods and management measures, ultimately achieving national pollutant discharge standards. Heavy metals generally exist widely in nature at natural concentrations, but due to the increasing exploitation, smelting, processing, and commercial manufacturing activities of heavy metals by humans, many heavy metals such as lead, mercury, cadmium, cobalt, etc. enter the atmosphere, water, and soil, causing serious environmental pollution and endangering human health!
According to the characteristics of heavy metal wastewater, the commonly used methods for treating heavy metal wastewater include chemical precipitation, redox treatment, solvent extraction separation, adsorption, membrane separation, and ion exchange. By treating it, measures such as turning toxicity into non toxicity, converting harmful substances into harmless ones, and recovering precious metals from it, and reusing purified wastewater, the discharge of heavy metals can be eliminated and reduced.
1. Chemical precipitation method
Chemical precipitation method is a method of converting dissolved heavy metals in heavy metal wastewater into insoluble heavy metal compounds, including neutralization precipitation method and sulfide precipitation method.
2. Oxidation-reduction treatment (chemical reduction method)
Cr in electroplating wastewater mainly exists in the form of Cr6+ions. Therefore, a reducing agent is added to the wastewater to reduce Cr6+to slightly toxic Cr3+, and lime or NaOH is added to produce Cr (OH) 3 precipitation and separation for removal. Chemical reduction method is one of the earliest applied treatment technologies for electroplating wastewater, which is widely used in China. Its treatment principle is simple, easy to control, and can withstand the impact of large amounts and high concentrations of wastewater. According to the different dosage of reducing agents, it can be divided into FeSO4 method, NaHSO3 method, iron filings method, SO2 method, etc.
Applying chemical reduction method to treat wastewater containing Cr, lime is generally used for alkalization, but there is a lot of waste residue; If NaOH or Na2CO3 is used, there will be less sludge, but the reagent usage will be high and the treatment cost will be high, which is the disadvantage of chemical reduction method.
3. Solvent extraction separation
Solvent extraction is a commonly used method for separating and purifying substances. Due to liquid-liquid contact, it can be continuously manipulated and has a good separation effect. When using this method, it is necessary to choose extractants with high selectivity. Heavy metals in wastewater generally exist in the form of cations or anions. For example, under acidic conditions, they undergo complex reactions with extractants, are extracted from the aqueous phase to the organic phase, and then re extracted to the aqueous phase under alkaline conditions, allowing the solvent to be regenerated for recycling. This requires careful selection of aqueous acidity during extraction manipulation. Although the extraction method has significant advantages, the loss of solvents during the extraction process and the high energy consumption during the regeneration process make this method have certain limitations and its application is greatly limited.
4. Adsorption method
Adsorption method is an effective method for removing heavy metal ions by utilizing the unique structure of adsorbents. Adsorbents for treating electroplating heavy metal wastewater by adsorption method include activated carbon, humic acid, sepiolite, glycan resin, etc. Activated carbon equipment is simple and applied in wastewater treatment

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