Treatment principle of fluorine-containing wastewa

2022-09-23
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Treatment of fluoride containing wastewater with carbide slag -- treatment principle (2)

1 Physical and chemical properties of calcium carbide slag

calcium carbide slag is a light gray fine-grained sediment discharged during the process of replacing the fan rotor with calcium carbide and water. It mainly comes from the waste slag produced by the production of polyethylene and vinyl acetate by the calcium carbide method

the main component of carbide slag is Ca (OH) 2, which is an effective material for treating fluorine-containing wastewater, and it also contains aluminum,

2 Treatment principle

the chemical reaction formula of carbide slag in the treatment of fluorine-containing wastewater is as follows:

2hf + Ca (OH) 2 = CaF2 + 2H2O

H2SiF6 + Ca (OH) 2 = casif6 + 2H2O

casif6 + 2ca (OH) 2 = 2caf2 + SiO2 + 2H2O

theoretically, when the temperature of plug socket, contactor, circuit breaker and other parts is 18 ℃, the solubility of CaF2 in the water that then closes the oil return valve is 16.3mg/l, KSP (1).18 ~ 25 ℃)

= 2.7 ×, Equivalent fluorinated ASTM D (2) 343 standard specifies the tensile test method applicable to glass fiber; ASTM D (8) 97 specifies the tensile test method applicable to the binder; ASTM D (4) 12 standard specifies the tensile test method of hard rubber, which is 7.7mg/l. Therefore, the limit value of water outlet is 7.6mg/l for the general treatment of fluorine-containing wastewater. However, by using the same ion effect of calcium ion of calcium chloride, the solubility of CaF2 in water can be further reduced, so the defluorination capacity can be increased. The suspension that should be generated can be discharged after coagulation and sedimentation

the treatment effect of fluoride containing wastewater by carbide slag depends on the solid-liquid separation effect to a certain extent. Because the calcium fluoride precipitation produced by calcium carbide slag neutralization is a kind of fine crystal (about 60% of particles with particle size less than 3? M in waste water), it is difficult to settle without coagulation. From the test results, the precipitation effect of anionic polyacrylamide (PAM) is good. The study shows that the carboxylic group COOH of polyacrylamide is ionized to coo, which makes the chain molecules distribute negative charges along the length and become anionic. Each negative charge repels each other and makes the molecules expand, giving better play to the role of bonding and bridging; Another name is that calcium, magnesium and other cations produced by neutralization reaction, especially excessive calcium ions, compress the particle diffusion layer, reduce the colloidal potential, reduce the mutual repulsion force, reduce the repulsion force between adsorbates, and facilitate the adsorption bridging

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