The Application of Sodium Sulfide in Electroplating Wastewater Treatment

Introduction

The electroplating industry plays a significant role in modern industry. Many tools in our daily lives are electroplated, which not only enhances their aesthetic appearance but also effectively delays rusting and other issues. Electroplating industry features diverse production processes, resulting in different types of wastewater discharges. These include acid and alkali pre-treatment wastewater, cyanide-containing wastewater from cyanide copper plating, copper-containing wastewater, nickel-containing wastewater, chromium-containing wastewater, and other heavy metal wastewaters. To treat these wastewaters, the chemical agent sodium sulfide is often utilized. This article will explore the effectiveness of sodium sulfide in treating electroplating wastewater.

Properties of Sodium Sulfide

Sodium sulfide, also known as smelly alkali, smelly soda, yellow alkali, red alkali, or sulfide alkali, is an inorganic compound. It has a strong hygroscopic property and is highly soluble in water. Its aqueous solution is strongly alkaline and can cause burns when it comes into contact with skin and hair, thus the name sulfide alkali.

Applications in Electroplating Wastewater Treatment

Sodium sulfide is effective in treating various metal pollutants in electroplating wastewater. It can handle not only copper in electroplating wastewater but also pollutants such as chromium, zinc, lead, nickel, and cyanide. When dealing with complex copper wastewater, a common approach is to add ferrous sulfate or other reducing substances under acidic conditions to break the complex. Then, adjust the pH to alkaline and add sodium sulfide. This process can reduce the amount of sodium sulfide used and prevent the formation and release of hydrogen sulfide gas under acidic conditions.

For free heavy metal wastewater, sodium sulfide can be directly added for treatment. However, for complex heavy metal wastewater, a pre-treatment to break the complex is required. Sodium sulfide hydrolyzes and reacts with complex heavy metal wastewater to form sulfide precipitates with very low solubility. These sulfide precipitates are not easily soluble even under acidic conditions. Therefore, using sodium sulfide to treat complex heavy metal wastewater has the advantages of low cost and good stability.

Considerations in the Use of Sodium Sulfide

One of the common issues in using sodium sulfide is the dosage. If the dosage is too low, the copper removal effect is not satisfactory. If the dosage is too high, it can darken the water body and increase the COD to a certain extent, polluting the water. To address this, before using sodium sulfide, it is necessary to adjust the pH value of the water to around 9. Additionally, conducting a beaker test in advance to determine the appropriate dosage can help avoid poor treatment effects or an increase in the COD content in the water.

Conclusion

Sodium sulfide has good treatment effects on heavy metal wastewaters from various industries such as printed circuit boards, metal smelting, electroplating, and dyeing. However, when using it to treat electroplating wastewater, we need to pay attention to the dosage and treatment process to maximize its advantages in treating wastewater while minimizing potential negative impacts. By carefully controlling these factors, sodium sulfide can be a valuable tool in the effective treatment of electroplating wastewater, contributing to environmental protection and sustainable development in the electroplating industry.