RU2164895C2 - Method of removing aluminum compounds from waste waters - Google Patents

Abstract

FIELD: waste water treatment. SUBSTANCE: treatment is effected with salts of phosphoric acids followed by separation of resulting precipitate by filtration or in settlers, said phosphoric acid salts more particularly being sodium tripolyphosphate, trisodium phosphate, sodium pyrophosphate, sodium hexametaphosphate, and potassium tripolyphosphate. Treatment is carried out within temperature range between 0 and 50 C at pH 6.5-8.5. Waste water treated under these conditions cam be used in cooling systems of recycling water supply plants. EFFECT: achieved complete removal of aluminum impurities and avoided pollution of water with scale-forming reagents. 2 tbl

Description

 The invention relates to methods for wastewater treatment, sent to the cooling water recycling system, namely to treat wastewater from aluminum compounds.

A known method of deposition of polyvalent metals, including aluminum, from aqueous solutions of 2-3% solution of sodium salt of carboxylmethyl cellulose in an equimolar amount relative to the concentration of polyvalent metals in the solution (Autosvid. USSR USSR N 808377, IPC C 02 F 1/58, publ. 1981)
However, the known method is very expensive, complicated, and when a macromolecular precipitant passes into the cooling water supply systems, bacterial suspension and mechanical suspensions of the reverse water may precipitate on the heat transfer surface of the condensation-refrigeration equipment, which is unacceptable under operating conditions of purge-free cooling systems.

Closest to the claimed technical solution is a method of reducing the aluminum content in drinking water and wastewater (German Application N 4441511, IPC 6 C 02 F 1/58, publ. 05.23.1996), which provides for the addition of calcium in water in an amount equimolar with respect to the aluminum contained therein for the formation of sparingly soluble calcium aluminate CaO · Al ₂ O ₃ · 10H ₂ O.

 The disadvantage of this method is the additional pollution of the treated water with calcium, which under the conditions of operation of purgeless water recycling systems exacerbates the problems of scale formation.

 The objective of the invention is the treatment of wastewater sent to feed the circulating water supply systems from aluminum compounds.

Aluminum salts are widely used in physicochemical wastewater treatment. Moreover, the treated effluent contains up to 0.5 - 1.4 mg / dm ^{3 of} residual aluminum.

When using this water to replenish non-purge cooling systems treated, for example, with a zinc-dichromate phosphate inhibitor, aluminum compounds form insoluble complexes with phosphate ions, causing clogging of the heat exchange equipment and cooling towers with aluminophosphate slurry, and thereby reduce the efficiency of the inhibitor. Permissible aluminum content in make-up water is 0.2 mg / dm ³ .

 The problem is solved in that the wastewater treatment from aluminum compounds is carried out by treatment with salts of phosphoric acids, followed by separation of the resulting dense precipitate by filtration or in sumps without filtration. Sodium tripolyphosphate (TPF), trisodium phosphate (THF), sodium pyrophosphate (PFN), sodium hexametaphosphate (GFN), potassium tripolyphosphate (PFC) are used as salts of phosphoric acids.

 Salts of phosphoric acids are used in an amount 2-20 times higher than the residual aluminum content.

The inventive method of wastewater treatment from aluminum compounds is carried out by the precipitation of aluminum compounds by phosphates at a temperature of from 0 to 50 ^o C and a pH of from 6.5 to 8.5. In this case, depending on the initial concentration of aluminum, phosphate and pH in aqueous solutions, many aluminophosphate complexes of the general formula precipitate
AlHy (PO ₄ ) _x ^{(3 + y-3x) +}
where "y" - varies from 1 to 2 depending on pH;
"x" - from 1 to 3, depending on the concentration of aluminum and phosphate from solid phases, and most often variscite Al (OH) ₂ HPO ₄ , sterrite [Al (OH) ₂ ] ₃ HPO ₄ · H ₂ PO ₄ , taranakite M ₃ Al ₅ H ₆ (PO ₄ ) ₈ · 18H ₂ O (M - monovalent ion) ^x , average aluminum phosphate AlPO ₄ .

 The resulting dense precipitates are insoluble in water, easily separated by filtration through sand filters or in sumps without filtration.

The inventive method of wastewater treatment is the cheapest, most effective and allows you to purify aluminum compounds from wastewater to the required standards - the aluminum content in the makeup water of purge systems is not more than 0.2 mg / dm ³ At the same time, a slight leakage of phosphates into the circulating system will contribute to the stability of mechanical suspensions in the volume of water.

 The proposed method for wastewater treatment from aluminum compounds is not described in the literature. The solution to this problem was achieved due to several special techniques, the combination of which is absent in the prototype, therefore, the invention meets the criterion of "novelty."

 When conducting a comparative analysis of the proposed method with similar technical solutions, it was found that such a combination of distinctive features and the achieved result is not described, which meets the criterion of "inventive step".

 The proposed method is as follows.

 After treatment with aluminum sulfate and flocculation, an aqueous solution of phosphate is introduced into the wastewater. After the formation of aluminophosphate complexes, water is purified on sand filters or in sedimentation tanks without filtration.

 Sodium tripolyphosphate (GOST 13493-86), trisodium phosphate (TU 2583-83), sodium polyphosphate (GOST 20291-80), sodium hexametaphosphate (2583-83), trisodium phosphate (GOST 201-76), potassium tripolyphosphate (potassium tripolyphosphate) were used as precipitating reagents. TU 113-08-631-88).

 The aluminum content was analyzed according to GOST 18165-89. When working out the optimal parameters of the cleaning process, the influence on the depth of cleaning of aluminum compounds of temperature and pH was taken into account.

 The pH of the wastewater was adjusted with 5% NaOH and HCl solutions.

 The proposed method is illustrated by the following examples.

 Example 1

With constant stirring in a glass of 1 dm ^{3 of a} sample of wastewater with a temperature of 5 ^o C, pH 6.5 (aluminum concentration of 0.97 mg / dm ³ ) 6.3 mg / dm ^{3 of} trisodium phosphate is added. After 10 minutes, the sample is filtered and the aluminum content in the water is determined.

 Examples 2-9.

 Carried out analogously to example 1. The process conditions and the results are shown in table N 2.

 From the data table. N 2 it follows that in the process of treating wastewater from aluminum compounds using salts of phosphoric acids, complete purification of water from aluminum is achieved.

Claims (1)

A method of treating wastewater from aluminum compounds, including treating with a chemical reagent and separating the precipitate formed, characterized in that phosphoric acid salts are used as a chemical reagent and the treatment is carried out at a temperature of 0-50 ^° C and a pH of 6.5-8.5.

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