Leather, such as the bags, leather sofas and leather clothes we use in our daily life, are all made of leather. However, during the production of these products, a large amount of wastewater is generated, and there are disadvantages such as a large discharge volume and numerous pollutants. The pollution mainly includes: heavy metals, suspended solids, oils, surfactants, etc. In this article, we will learn how leather wastewater is generated and how it should be treated.
In some of the industries with severe pollution in our country, the leather industry is one of them. When processing leather, animal skins are used as raw materials, which are then chemically treated and mechanically processed to complete the process. During this manufacturing process, the main sources of leather wastewater from the product include: deashing, dehairing, softening, degreasing, water washing, water squeezing, dyeing, etc. The suspended solids mainly come from: a large amount of lime, oil residue, meat residue, etc. COD mainly comes from sources such as sodium sulfide, acids, ammonium salts, proteases, and alkalis, which are produced during the usage process. BOD is produced by soluble proteins, blood and other organic substances. Heavy metal chromium is mainly the chromic acid wastewater discharged during the chromium tanning process.
So, how should leather wastewater be treated?
This needs to be determined based on the type of leather. Different leather processing wastewater treatment methods will also vary, so as to achieve good results. The more common ones include oil-alkali precipitation method, direct circulation method and extraction method, etc. Here is a brief introduction to the working principles of these three methods.
1.Alkali precipitation method: This method involves first adding alkali to the wastewater, then flushing the wastewater to recover chromium hydroxide, and acidifying the chromium sludge for reuse. Sodium hydroxide is usually used more frequently as a precipitating agent. During this production process, the chromium mud recovered by this method contains hard-to-remove oils and proteins, etc. These cannot be recycled or may affect the quality of the leather during the recycling process.
2.What is the direct loop method? This method mainly involves using the waste chromium solution after filtration and online water quality monitoring for the next batch of bare skin pickling acid solution, or further adjusting the pH value and supplementing chromium salts for tanning. Through this method of recycling and reuse, chromium salts can be well utilized. This not only saves the consumption of chromium salts but also reduces the chromium content in wastewater, thereby alleviating its treatment burden. However, if the leather is recycled too many times, it will cause impurities to accumulate, thereby affecting the quality of the leather. To solve this problem, methods such as heating and adding new electrolytes are all acceptable.
3.If you are using the extraction method,it involves the use of a specific extractant. During this process, the pH value of the extraction system should be controlled at around 4.0. Additionally, H+ ions in the extraction solvent and chromium ions in the waste liquid will be exchanged under alkaline conditions (in a certain proportion). The advantage of this method is that the trivalent chromium ions recovered by this method have a high purity and a promising application prospect.
Attached Text
Question: If I conduct real-time monitoring of heavy metal chromium in wastewater, what instrument should I use?
Answer: The T8000-Cr Total Chromium Online Analyzer can be used. This instrument determines the content of heavy metal chromium in it by acid oxidation and colorimetry with a characteristic chromogenic reagent after masking interference ions.
