Views:12 Author:Site Editor Publish Time: 2017-02-05 Origin:Site
Electroplating wastewater composition is very complex, with the exception of cyanide (CN-) wastewater and acid-base wastewater, the heavy metal wastewater is electroplating potentially hazardous waste water category. According to the classification of heavy metal elements contained in heavy metal waste water, it can be generally classified into three categories: chromium (Cr), nickel (Ni), cadmium (Cd), copper (Cu), zinc (Zn) Gold (Au) wastewater, silver (Ag) wastewater and so on. In general, the acidity of water is strong, there are a small amount of alkaline, in which the heavy metal acid and alkali content with its surfactants, brightener, and production processes vary.
Electroplating plastic water, the general content of heavy metals is relatively low, depending on the processing of metal objects and the number of plating, but usually the chromium content of electroplating water are relatively high, as the treatment methods are the following, mainly based on cost and water requirements of the method.
1. chemical precipitation:
Chemical precipitation method is a method for converting heavy metals in the dissolved state into a water-insoluble heavy metal compound, which includes neutralization precipitation method and sulfide precipitation method.
2. and precipitation method:
In the waste water containing heavy metals by adding alkali for neutralization reaction, so that heavy metals generated in water-insoluble hydroxide, precipitated form to be separated. Neutralization and precipitation method is simple, is commonly used in wastewater treatment methods. Practice has proved that the operation need to pay attention to the following points:
(1) in the sedimentation, the wastewater if the pH value is high, the need for neutralization before discharge;
(2) There are many kinds of heavy metals in waste water, when the waste water containing Zn, Pb, Sn, Al and other amphoteric metals, the pH value is high, there may be redissolving tendencies, so strictly control the pH value, the implementation of sub-precipitation ;
(3) some anions in wastewater, such as: halogen, cyanide, rot, and so may form complexes with heavy metals, and therefore need to be in before and after pretreatment;
(4) some particles are small, difficult to precipitate, you need to add flocculants to help precipitate generation.
3. sulfide precipitation method:
Adding sulfide precipitating agent to make heavy metal ions in waste water to generate sulfide precipitation removal method. Compared with the neutralization precipitation method, the advantages of sulfide precipitation method are: the solubility of heavy metal sulfide is lower than the solubility of its hydroxide, and the pH value of the reaction between 7-9, the treated wastewater is generally not neutralized. Sulfide precipitation method of the shortcomings are: sulfide precipitate particles small, easy to form colloidal; sulfide precipitation agent itself in the water residue, case of hydrogen sulfide gas generated by the acid, resulting in secondary pollution. In order to prevent secondary pollution problems, the authors have developed improved sulfide precipitation method, that is, in the wastewater to be treated with the selective addition of sulfide ions and another heavy metal ions (the heavy metal sulfide ion concentration than the need to remove the balance Of the heavy metal pollutants of the sulfide concentration of high equilibrium). Since the added heavy metal sulphide is more soluble than the heavy metal sulphide in the waste water, the heavy metal ions in the wastewater are separated from the added heavy metal ions and prevent the generation of hydrogen sulphide and the problem of sulfide ion residue .
4. chelate precipitation method:
A chelating precipitant (e.g., DTCR) is added to cause chelating precipitation. The method has the advantages of stable effluent compliance, good application conditions, no secondary pollution, low water content of sludge, easy recovery of sludge, simple equipment requirement and convenient implementation. The disadvantage is the high price.
5. redox treatment:
Chemical reduction method: chemical reduction method of electroplating wastewater treatment is one of the earliest application of governance technology in China has a wide range of applications, the management principle is simple, easy to master, can withstand large amounts of water and high concentrations of wastewater impact. According to the different adding of reducing agent, can be divided into FeSO4, NaHSO3, iron scrap, SO2 and so on.
The use of chemical reduction method to deal with the treatment of wastewater containing Cr, alkaline lime generally used, but the residue more; with NaOH or Na2CO3, the sludge is small, but the high cost of chemicals, treatment costs, which is the shortcomings of chemical reduction method.