Pickling is an indispensable step in the purification of high-purity quartz sand ore, especially high-purity quartz sand raw material for photovoltaic glass. Quartz is insoluble in acid and other impurity minerals can be dissolved by acid solution to realize the beneficiation and purification of quartz. Common acids include hydrofluoric acid, sulfur H2SO4 acid, hydrochloric acid, oxalic acid, nitrate HNO3 acid, etc. The acid concentration of various acids depends on the type and content of impurities in quartz sand.
Although the removal rate of impurities in acid washed quartz sand is higher, once the wastewater after removal is not properly treated, it will have a serious impact on the environment, soil, etc. There is a large amount of H, F -, SO4 -, Cl -, C2O42 -, NO3 plasma left in the pickling waste liquid. If it is directly discharged without treatment, it is easy to cause serious consequences such as environmental, soil and groundwater pollution, as well as underground pipeline corrosion, especially fluoride pollution and fluoride ion corrosion. Therefore, the wastewater after acid cleaning of quartz sand shall be strictly treated and can only be discharged after reaching the national discharge standard. For example, according to the current sewage discharge standard GB8978-1996, the mass concentration of F - in the discharged water shall not exceed 10mg/L.
However, in a series of processes of pickling wastewater treatment, the residual acid has seriously corroded the treatment facilities. Conventional heavy anti-corrosion coatings such as epoxy and vinyl can no longer meet the protection requirements, and are often destroyed in a mess within half a year. At this time, Zhisheng Weihua special acid resistant coating rose to the challenge. After two years of practical application verification, it successfully withstood the corrosion of hydrogen ions and various acid radical ions. It is expected that it will still be no problem after two or three years of service.
The sand washing wastewater to be treated mainly includes acid washing sediment, deacidification wastewater, tank washing wastewater, dehydration wastewater after washing, filtration wastewater of quartz sand storage, etc.
Sand washing wastewater treatment facilities requiring acid resistant coating protection mainly include raw water tank, regulating tank, sedimentation tank, neutralization tank, sand filter, etc.
Zhisheng Weihua Group has been working in the field of special wastewater treatment and protection for many years, specializing in the corrosion protection of special acid-base media, special intermediates, complexes, etc., and has developed a series of special anti-corrosion coatings, especially ZS-1033 hydrofluoric acid (HF) resistant anti-corrosion coating, which has become a star product for long-term protection of pickling equipment and wastewater treatment facilities.
ZS-1033 special acid resistant coating is made of more than 20 kinds of materials, such as phenol formaldehyde plus fluorine densification modified resin, barite, nano graphite flakes, etc. The cured coating has high inertia, large chemical steric resistance, density, acid and alkali resistance, low moisture permeability coefficient, and strong anti-corrosion performance. It can prevent the corrosion of hydrofluoric acid of various concentrations, and can also resist the corrosion of various strong acids, strong bases, salts, intermediates, and organic additives, such as hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, phosphoric acid, NaOH, soda ash, ammonia, sodium chloride, calcium chloride, etc.
When hydrofluoric acid is used as the main pickling medium, F ion removal is mainly considered for wastewater treatment. The current treatment methods mainly include precipitation method and adsorption method. There are mainly two different treatment processes according to the fluoride concentration.
① Low concentration fluoride wastewater: generally, flocculation sedimentation method or adsorption method can be used directly.
② High concentration fluoride wastewater: add lime milk to precipitate calcium fluoride, which can reduce the fluoride content to below 50mg/L, and then add flocculant to reduce the fluoride content to below 10mg/L.
The main pollution factor of pickling wastewater is F -, and the main process is to add Ca2, convert fluoride into sediment, and remove it through coagulation and sedimentation. The treated wastewater meets the discharge standard or is reused. This design process is mainly divided into two stages of sedimentation: the first stage sedimentation removes most of the fluoride ions in the wastewater, and the treatment capacity reaches more than 90%; The secondary precipitation removes fluoride ions to less than 10 mg/L, meeting the emission requirements of fluoride ions.
In most pickling sand wastewater treatment processes, ZS-1033 hydrofluoric acid resistant anti-corrosion coating can be used for protection of various metal tanks (tanks) and other equipment, while ZS-1011 oily transition coating is used for priming of concrete tanks before ZS-1033 coating. For other tanks with high acid and alkali dosing concentration, ZS-1032 strong oxidation resistant anti-corrosion coating or ZS-1034 acid and alkali resistant anti-corrosion coating can be selected. The coating design scheme of each project can be further communicated with AIG.
