Study on Treatment of Various Mixed Acid Waste Washes in Metal Products

 

Study on Treatment of Various Mixed Acid Waste Washes in Metal Products

Liu Zongyi      Liu Yi        Xu Jing

(Shaanxi Environmental Science Research Institute) (James Cook University) (Xi'an Huanke Water Treatment Co., Ltd.)

Summary    The treatment of pickling waste liquid in the steel industry and metal products production process has always been a difficult problem in environmental protection. In recent years, with the increase of production varieties, the composition of acid washing liquid has increased from monoacid to various mixed acid, and the research method of mixed acid waste washing liquid has been reported. at least. For the first time, the acid washing solution and treatment method are systematically described.

Key words   metal products    Mixed acid    Pickling solution

1. Steel plate, pipe production and metal products

Pickling and surface treatment require pickling. With the development of science, the metal material changes, and the pickling liquid transitions from a single acid solution to a mixed acid solution and a complex acid solution. Single acid waste acid solution has always been an environmentally friendly problem. Complex acid and complex acid treatments are more difficult. In order to solve the processing problems, it is necessary to have a relatively complete and systematic understanding of pickling technology and pickling waste liquid.

1 , pickling technology and pickling waste characteristics

1.1 , the pickling equipment is expanded, and the amount of waste acid washing liquid is increased.

    With the development of pickling technology and market competition, the demand for scale benefits, many pickling enterprises have developed from pickling tanks to pickling units, and the discharge of waste acid washing liquid has increased from several tons per day to several tens of tons or even hundreds of tons. Under the requirements of environmental protection policies, the problem of disposal of waste acid washing liquid is the first problem solved by enterprises.

1.2 , pickling material changes lead to complex composition of pickling solution

Due to changes in the product market, the pickling material has been developed from a single carbon steel, stainless steel, to alloy steel such as chrome steel, manganese steel, and nickel steel. The composition of the pickling solution is developed from a single acid washing solution to 2 - 4 mixed acids, and some chemicals are added to the mixed acid.

additive. Undoubtedly, the complex components of mixed acid increase the difficulty of processing.

1.3 , the development of pickling technology increases the difficulty of treatment of waste acid washing liquid

In order to ensure the pickling effect, many companies add some auxiliary processes before pickling, such as: shot peening, degreasing, high, medium and low temperature rust removal. These ancillary processes add to the difficulty of handling the spent acid wash, increasing processing equipment and processing costs.

1.4 , waste acid wash treatment trend changes

    A single acid solution using a pickling unit with a large amount of emissions is usually recovered by a commercial acid supply unit, and a company with a small amount of emissions uses a hoarding method to transfer the waste acid washing liquid. Changes in the production variety, a variety of mixed acid and waste acid washing liquid containing detergent, commercial acid suppliers refused to recycle, waste acid washing liquid became a hot "mountain", the original processing channels have changed. The treatment of various pickling wastes is more difficult and there are fewer researchers. Environmental engineering companies usually use passive lime neutralization.

2 , metal product production wastewater treatment process

2.1 , steel belt production process

The production process of metal products is different, and the wastewater generated is also different. In order to prove the wastewater treatment process, a representative steel strip production process is selected for explanation.

2.1.1 . The cold-rolled sheet is pickled with hydroxide steel or degreaser before pickling to remove the surface grease.

2.1.2 , pickling liquid According to the material of the product, using monoacid (hydrochloric acid-based) mixed acid (hydrochloric acid, hydrofluoric acid or nitric acid), steel pipe is mostly phosphoric acid, pickling method is divided into: pickling unit, pickling tank, daily Waste acid emissions are small.

2.1.3, a large amount of washing waste, the waste is usually acid 4 - A 5-fold washing waste PH value is generally 3 - between 4.

2.1.4 After the metal products are processed, emulsification is carried out as needed to produce an emulsified waste liquid.

2.2 , steel belt production wastewater treatment

In environmental engineering, the principle of wastewater treatment is comprehensively treated for pollutants with the same chemical properties, and the pollutants with different chemical properties are treated separately, and then the wastewater is comprehensively treated.

2.2.1 . Degreasing wastewater and oxidizing wastewater are treated by oil-water separator. The separated waste oil is recovered from the oil chemical plant, and the alkaline wastewater is integrated into the sewage station.

2.2.2 . The pickling waste liquid is treated by an acid recovery machine, and the recovered regenerated acid is returned to the pickling process to be re-used with a new acid. 4. Neutral weak acid wastewater enters the sewage station for comprehensive treatment .

2.2.3 . The sewage station can be used for flocculation, pressure filtration and sludge to obtain products such as iron yellow or iron hydroxide.

3 , worthy of attention

3.1 , misunderstanding of wastewater treatment

Some enterprises believe that as long as the waste acid washing liquid is treated, the PH value is neutral, instead of sewage treatment, some enterprises also need to comprehensively treat the degreasing wastewater, waste acid liquid, washing wastewater, emulsion, and mixing together. These processes are not feasible and cannot be achieved. The acid recovery technology and equipment are only one part of the treatment process in the industrial wastewater of metal products production, and can not be used to treat the entire enterprise wastewater.

3.2 , the direction of regenerative acid

Since the acid recovery technology has been used in recent years, many design units have not designed regenerative acid recycling devices in the production process. How to digest the residual acid in the waste acid washing liquid, especially the multiple mixed acid destinations, is the first consideration for enterprises. The problem.

3.3 , metal products, monoacid waste acid wash features

The pickling process in the production of metal products is mainly to remove metal oxides, commonly known as "oxidation scale". The metal product pickling waste liquid has a single component, mainly the metal material itself and the material added elements. Therefore, the salt components in the waste liquid are not too complicated, and the metal ions are mostly divalent ions, and the separation effect is obvious, and no more pretreatment equipment is needed.

3.4 , a variety of mixed acid waste acid wash features

The environmental engineering treatment usually uses the alkali neutralization method for the waste acid solution to change the pH value of the solution to reach neutrality. The treatment of general waste acid washing liquid with lime milk is not easy to manifest. In addition to the waste of cost, there are no Other technical problems , and various mixed acid waste liquids are different . The pollution of single acid waste liquid is only PH and Fe , and there are no other projects. In addition to P H and Fe metal ions, a variety of mixed acid waste acid washing liquids also have special ions such as F , P , NOx anions and chromium, nickel, zinc, etc., and some pretreatment equipment needs to be added.

4 , the conclusion

Waste acid recovery is the need of sustainable development, and is also the inevitable outcome of scientific development, the result of market competition. Metal processing steel, steel, aluminum and other metal processing acid recovery, only a small part of acid recovery technology, in hydrometallurgy (vanadium, molybdenum, chromium, zinc, etc.), bio-pharmaceutical, quartz products, non-metallic products (graphite , molybdenum disulfide, silicon carbide, silica gel, etc.), environmental protection (smoke and acid), rare earth industry and other fields have a wide range of applications.

Waste acid recovery is an emerging science. Due to different products and different acid types, the difference between metal and non-metal salts in waste acid liquid is very large. Therefore, small tests and special designs are needed for each project, for enterprises and environmental protection departments. It is a new topic and needs further research.

Company Name: Xi'an Huanke Water Treatment Co., Ltd.

Contact: He Min

Contact number: 029 - 88321607

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