Process for separating nitrates, COD salts and sulfates by evaporating wastewater containing nitrates, COD salts and sulfates

Abstract

A process for separating nitrates, COD, salts and sulfates by evaporating wastewater containing nitrates, COD salts and sulfates is provided. The process includes A) performing evaporation concentration on wastewater containing salts and sulfates and adopted as a raw material to obtain fresh water and a concentrated solution; B) evaporating the concentrated solution to obtain salts or sulfates, fresh water and a salt-sulfate saturated solution; C) evaporating the salt-sulfate saturated solution to obtain a salt-sulfate mixture and a mixed salt mother liquor, drying the mixed salt mother liquorto obtain mixed salts containing nitrates, reductive compounds corresponding to CODs, salts and sulfates; D) dissolving the salt-sulfate mixture with the wastewater to obtain a mixed salt solution; E) evaporating the mixed salt solution at 40-140 DEG C and crystallizing to obtain sulfates or salts, and a circulating mother liquor for sulfate or salt preparation; F) allowing the circulating motherliquor for sulfate or salt preparation to participate in evaporation in the next cyclic process step B at an evaporation temperature of 40-140 DEG C to evaporate, crystallize and precipitate salts orsulfate and to obtain a circulating mother liquor for salt or sulfate preparation, with the circulating mother liquor for salt or sulfate preparation participating in evaporation in the step E of thenext cyclic process.

Description

technical field [0001] The invention belongs to the technical field of inorganic chemical industry, in particular to a process for evaporating and separating nitrate-COD salt-nitrate wastewater containing nitrate-COD salt-nitrate. Background technique [0002] COD is chemical oxygen demand. It is the amount of oxidant consumed when a certain strong oxidant is used to treat water samples under certain conditions. It is an indicator of the amount of reducing substances in water. Reducing substances in water include various organic matter, nitrite, sulfide, ferrous salt, etc. Therefore, chemical oxygen demand (COD) is often used as an indicator to measure the content of reducing substances in water. Known processes for separating COD salt nitrate from COD salt nitrate wastewater include: [0003] 1) After complex pretreatment, the wastewater is concentrated by membrane method (reverse osmosis, electrodialysis, etc.), and the concentrated solution is separated by nanofiltratio...

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Problems solved by technology

[0006] Among the above-mentioned processes, process 1) has problems such as complex process flow of wastewater pretreatment system, adding chemicals, and large amount of miscellaneous salts; process 2) has complex process process of wastewater pretreatment system, adding chemicals, large refrigeration energy consumption, Glauber's salt decahydrate needs re-evaporation and denitrification, and the amount of miscellaneous salts is large; process 3) there is a complex process flow in the wastewater pretreatment system, adding chemicals, refrigeration equipment and cold energy consumption, and the COD of the frozen mother liquor corresponds to reducing substances and calcium It is difficult to remove the enrichment of magnesium ions in circulation, and the amount of miscellaneous salts is large, etc.

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