Industrial waste salt comes from industrial production, high-salt wastewater treatment, pesticide production, etc. will produce a large amount of industrial waste salt, mainly refers to the solid waste with inorganic salt as the main component, the annual output of waste salt exceeds 2.0×107t, mainly divided into chlorine There are two types of sodium chloride and sodium sulfate.

Divided by industries of pesticide industry (30%), pharmaceuticals (10%), fine chemicals (15%), printing and dyeing (45%), in Jiangsu Province, salt-containing wastes mainly come from dye intermediates (HW12), Pharmaceutical intermediates (HW02), pesticide intermediates (HW04), coal chemical industry (HW11) and hydrometallurgy (HW48).

According to the composition of industrial waste salt, industrial waste salt can be divided into single salt and mixed salt. A single salt is a salt with a single component; a mixed salt refers to a salt with two or more components, and the organic content in the industrial waste salt is related to the production industry. A survey in Jiangsu shows that among the waste salt temporarily stored in the industrial park, mixed salt accounts for 80%, and the remaining 20% ​​is single salt.

Industrial waste salt has the characteristics of complex composition, wide range of sources and high toxicity. Although it is not listed separately in the hazardous waste list, the 2016 National Hazardous Waste List clearly lists the distillation and reaction generated in the production process of chemically synthesized APIs. Residues, waste mother liquors and reactive base wastes generated during the production of chemically synthesized APIs are classified as hazardous wastes. Therefore, industrial waste salt not only destroys the ecological environment, but also harms people and animals. Once the soluble salt and impurities in the polluted salt seriously cause soil salinization, it will endanger the survival and development of surrounding agriculture, forestry and animal husbandry, and even cause serious pollution to surrounding water sources and groundwater. Dangerous.

In view of the nature of industrial waste salt, it needs to be properly disposed of. In foreign countries, most of this by-product waste salt is directly dumped into the ocean after harmless treatment. This treatment method has great limitations. First, Enterprises must be near the sea or not far from the coast. Second, the by-product polluted salt does not contain harmful organic and inorganic impurities. In fact, the by-product polluted salt in chemical production depends on the product, and the composition of polluted salt is also different, and sometimes there is a big difference, which makes the treatment and utilization of by-product polluted salt more difficult.

Domestic industrial waste salt disposal technologies include: landfill method, high temperature oxidation method, salt washing method, etc. At present, landfill method is the main disposal method of industrial waste miscellaneous salt in my country, but there are the following problems in waste salt landfill:

(1) The investment is large. The land occupation is mostly based on the relevant regulations of the pollution control standard for hazardous waste landfills. Waste with a total water-soluble salt content of ≥ 10% cannot enter the flexible landfill, so the waste salt must enter the rigid landfill. For the same scale of landfill, the investment of rigid landfill is larger than that of flexible landfill, and the floor area is relatively large.

(2) There are few rigid landfills in China. At present, most landfills in China are flexible landfills, and the landfill of waste salt is limited, and most of the waste salt in enterprises has no way to landfill.

(3) The cost of landfill is high. At present, the landfill ton cost of waste salt is as high as more than 4,000 yuan, which is unbearable for enterprises. To sum up, industrial waste salt is not easy to be landfilled, so it is recommended to use it as a resource.

According to the source of waste salt, industrial waste salt contains highly toxic organic matter. Whether for single salt or mixed salt, to realize waste salt resource, the organic matter in waste salt must be removed first, and then the salt is separated.

01 Go Organics

According to the content of organic matter in waste salt, its disposal technology is commonly divided into two categories:

(1) High temperature oxidation method

In view of the high organic content in waste salt, this method treats waste salt at high temperature, so that organic impurities in waste salt are oxidized into CO2, CO, H2O gas at high temperature, so as to achieve the purpose of removing organic impurities. The key of this method is decomposition and oxidation. Choice of combustion equipment.

(2) Salt washing method

The salt washing method cleans the saturated by-product solution, and dissolves the organic matter and other substances in the by-product in the cleaning solution, so as to achieve the purpose of purifying the by-product. This method is more suitable for by-product waste salt with less impurity content and single impurity composition.

02 Mixed salt separation

The mixed salt obtained by removing the organic matter is still an inorganic substance with various components, such as sodium sulfate and sodium chloride, potassium chloride and sodium chloride, potassium chloride, and needs to be further processed to obtain a single salt, and the separation of the inorganic salt requires the help of three The element system phase diagram analysis can analyze the relationship between the material content in the whole evaporation process, which can be determined by the lever rule.

By applying the fatty alcohol/salt/water two-phase system to the separation of potassium chloride and ammonium chloride mixed solution, Shi Xuna developed a new method for separating potassium chloride and ammonium chloride mixed solution, namely n-propanol – Potassium chloride-ammonium chloride-water two-phase system. The method is low cost and the solvent is easy to recover.

Actively promote the technical specifications of waste salt disposal, and carry out the application exploration of industrial waste salt recycling projects. For example, in a new industrial waste salt recycling project, the raw material of industrial waste salt comes from a chemical industry park. There are two types of industrial waste salt, which use different craft.

TOC ≤ 3600ppm of industrial waste salt, the process plan is to regenerate raw sewage salt and washing liquid through countercurrent washing, and the wet salt is centrifuged and dried to obtain product salt, including storage of sewage salt, sewage salt regeneration unit, brine evaporation unit, and wastewater treatment. system.

The washing liquid and the polluted salt are fully mixed in proportion and washed under the action of an external field; the high-salt sewage from the polluted salt regeneration process by the brine evaporation unit is evaporated and crystallized to separate the salt crystals in the material and return to the polluted salt. The regeneration process continues to regenerate, producing high COD wastewater and sending it to the sewage treatment process.

Industrial waste salt with TOC > 3600ppm is directly incinerated by incinerator to remove organic matter, including solid feeding system, incineration system, waste heat recovery system, and flue gas purification system.

01 Incineration system

02 Waste heat boiler

03 Flue gas purification system

Taking into account comprehensively, the feasible solutions for the recycling of industrial waste salt are suggested as follows:

Single waste salt with low organic content: salt washing + impurity removal (removal of impurities and salt separation) + crystallization to obtain salt that meets national product standards;

For high organic content, large scale and mixed salt: stable operation of high temperature oxidation + impurity removal (impurity removal and salt separation) + crystallization to obtain salt that meets national product standards.

At the same time, with the continuous investment of industrial waste salt recycling projects, the existing processes and equipment problems will be continuously improved and perfected, and a mature and stable resource utilization technology will be formed for industrial waste salt in the future.