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Treatment of COD Problems in Electroplating Wastewater Production and Discharge Process

by:BOQU     2022-09-18

There are many inorganic substances in electroplating wastewater, which contain a variety of heavy metal ions; there are also many organic substances, and all organic substances have two common characteristics: one is that organic substances are at least composed of carbon and hydrogen; the other is that most organic substances can occur. Chemical oxidation or microbial oxidation, the more organic matter in the wastewater, the more oxygen consumption.

Electroplating wastewater COD production. Sewage characteristics The electroplating process is generally divided into three parts: pre-treatment, electroplating, and post-treatment.

These three parts all use some organic substances. In the subsequent washing process, these organic substances will enter the washing water, and finally enter the discharged wastewater, which constitutes the COD index.

(1) The function of the pre-treatment process is to level, degrease and rust the workpiece to be plated. Polishing paste is often used in the process of polishing and polishing the workpiece. The polishing paste is made of grease and paraffin. Cleaning these grease and paraffin will produce wastewater with high COD.

The chemicals used in the degreasing process in the past include sodium hydroxide, sodium carbonate, trisodium phosphate, and sodium silicate.

In recent years, in order to improve the speed and quality of oil removal while reducing the temperature during oil removal, surfactants are commonly used.

Most types of surfactants are compounded by anionic surfactants and nonionic surfactants.

Anionic surfactants can use sulfate fatty salts (such as sodium lauryl sulfate); non-ionic surfactants can use condensation products of ethylene oxide and certain hydrophobic compounds (such as fatty alcohol polyoxyethylene ether).

These surfactants are all organic. The rust removal process uses a lot of hydrochloric acids, sulfuric acid, and corrosion inhibitors. Although hydrochloric acid is not an organic substance, the Cl- that constitutes hydrochloric acid will increase the COD index.

The Fe2+ generated by pickling steel will also increase the COD index. Frequently used corrosion inhibitors (such as hexamethylenetetramine. Thiourea) are also organic, and will also increase COD.

(2) In the past, inorganic substances were used for electroplating, for example, zinc oxide was used for zinc plating, copper sulfate was used for copper plating, and nickel sulfate was used for nickel plating.

The main brighteners used in bright zincate zinc plating are organic aldehydes and ketones, and the auxiliary brighteners are commonly organic heterocyclic compounds.

There are many kinds of bright acid copper plating additives, including unsaturated organic sulfides and surfactant compounds (such as polyether compounds, organic sulfides with sulfonic acid groups, etc.).

The fourth-generation additive for nickel plating consists of pyridine derivatives, derivatives and their epoxy condensates or sulfonated products.

(3) In the post-treatment process of electroplating, in order to improve the corrosion resistance of the coating, sealing treatment is often performed, and some sealing agents are also organic.

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