Advantage analysis of calcium hydroxide in sewage treatment

Advantage analysis of calcium hydroxide in sewage treatment

   Analysis of the advantages of calcium hydroxide wastewater treatment: 1. The alkaline neutralizer in wastewater is mainly consumed in the following four aspects: 1. Neutralize free acid in wastewater; 2. Neutralize acid salt in wastewater; 3. Provide hydroxide ions to react with metal ions directly to form insoluble hydroxide precipitate; 4. Adjust the pH value to alkaline to obtain conditions conducive to the precipitation of metal hydroxide. In the process of treating acid-base wastewater by chemical precipitation, the control of pH value is a very important factor. 2. At present, there are mainly three kinds of alkaline neutralization agents: sodium hydroxide, sodium carbonate and calcium hydroxide. Sodium carbonate: sodium carbonate, sodium hydroxide, namely sodium hydroxide, calcium hydroxide, is also known as hydrated lime Ca (OH) 2. 3. The main factors to be considered in the selection of reagents are: price, reaction speed, dosage, cost of storage and preparation device, difficulty of transportation and final product after chemical reaction. In terms of price, under the same treatment effect, the ratio of sodium hydroxide, sodium carbonate and calcium hydroxide is 48:100:13; in terms of reaction speed, sodium hydroxide > sodium carbonate > calcium hydroxide; in terms of coagulation and decolorization effect, sodium hydroxide < sodium carbonate < calcium hydroxide; in terms of dosage, storage and preparation device cost, sodium hydroxide < sodium carbonate < calcium hydroxide; in terms of reaction generation For the product, calcium hydroxide is the most easy to dehydrate. When sodium hydroxide is used for neutralization, a large number of sludge will be produced which is thick and difficult to precipitate, while sodium carbonate will generate foaming problems due to the release of CO2 generated. By comprehensive comparison, the neutralizing agent is generally lime milk, which is the emulsion of calcium hydroxide. It is recognized as the first choice of alkaline neutralizer.

   Calcium hydroxide as acid water treatment agent can effectively remove anions such as phosphate, sulfate and fluoride. In practical operation, we usually use lime milk (calcium hydroxide solution) as dephosphorization agent, because in addition to coagulation sedimentation and acid neutralization, Ca (OH) 2 as coagulant has a good coagulation effect, which also has a good removal effect on other pollutants.

   Under the alkaline condition, when the pH value is about 10, the phosphate content in the water is the lowest, and the phosphorus removal effect is the best. The effluent can meet the requirements of the national integrated wastewater discharge standard (gb89781996) that the mass concentration of phosphate is less than 1.0mg/l. The fluorine-containing wastewater mainly comes from non-ferrous metal, rare metal smelting, glass ceramics manufacturing, chemical fertilizer and pesticide, stainless steel pickling, silicon parts cleaning and other production processes, but the fluorine content of fluorine-containing wastewater in different industries is quite different. Most of the mixed wastewater containing a large number of other pollutants except Fluorine are treated without recovering fluorine. For this kind of wastewater, experts generally believe that two-stage treatment is necessary to make the residual fluorine concentration less than 10mg / L. Lime is the standard method to reduce the high concentration of fluoride ions in the first treatment, and the residual fluoride concentration after treatment is usually 15-40mg / L. However, it has also been reported that when there are a large number of multivalent metal ions in the water, it will produce the same effect as the multivalent metal ion addition method, and the high concentration fluorine-containing wastewater can also be treated to a fluorine concentration of less than 10mg / L through primary lime treatment. In addition, when the water contains calcium chloride, calcium sulfate and other salts, the solubility of calcium fluoride is reduced due to the same ion effect, and the concentration of fluorine can also be reduced to less than 10mg / L or even to less than the theoretical solubility of calcium fluoride through primary lime treatment.

   Calcium hydroxide has a great advantage in water treatment both in price and treatment capacity.