SU1057434A1 - Method for purifying effluents method for purifying effluents from ions of hexavalent chromium - Google Patents

Abstract

A METHOD FOR CLEANING WASTE WATER FROM SIXIVALENT XRSMA IONS, including treatment with a reducing agent, precipitation and oh; sludge division, characterized in that in order to reduce the residual content of hexavalent chromium ions in water, to increase the sediment filterability and reduce the consumption of sludge. The treatment with a reducing agent is carried out to an equal ratio of hexavalent and trivalent chromium ions in the water to be purified, and the precipitation is carried out at a pH of 6.0-7.0,

Description

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4 The invention relates to wastewater effluent and can be used in the purification of chromium-containing solutions in the engineering, chemical and other industries. The ion-exchange purification method 1 is known; the chromator or bichromate ipnov sorption is enclosed in the sorbts on strongly basic anion exchangers of the AB-17 type. This process can be expressed by the following equation 2 A OH CniOj-A jCr207 + 20H However, this method has not been applied due to the high cost of ion-exchange resins and their significant deficiency. The closest to the proposed technical essence and the achievable result is a method of purifying wastewater from six valence chromium ions, which includes treatment with a reducing agent, sedimentation and separation of sludge. Sulfur dioxide, hydrazine, sodium sulfite and sodium bisulfite, sodium sulfide, etc. are used as reducing agents. When interacting with a reducing agent, trivalent chromium ions are formed, which precipitate as insoluble hydroxide C.gr (it is at pH 8-9 2. The disadvantages of this method are the high residual content of chromium ions, low MOCTt filtering of the precipitate and pain (Shy reagent consumption The purpose of the invention is to reduce the content of hexavalent chromium ions in water, to increase the filtering of the precipitate and reduce the consumption of the reducing agent. The goal has been achieved by the method waste water treatment of hexavalent chromium ions, which include treatment with a reducing agent, sedimentation, sediment separation, treatment with a reducing agent, lead to an equal ratio of hexavalent ions and three portions; - ribbon chromium, and precipitation lead njpH pH 6.0-7.0. Chrome-containing aqueous solutions are treated in a static mode, the reduction of hexavalent chromium ions is made by ROB; only that in the resulting system; an equal amount of chromium ions (yi) and chromium (1) is applied; system 1y up to values of 6.0-7.0 poorly soluble xpow thromate complex - ,; easily o /, del.emye mechanical method, for example, MG-R filtering. The chemistry of the process of the proposed method can be presented as follows C.Ch1res34sp 4 CHO g. The fact that during the processing hydroxychromochromatic complexes Cr (OH) NSgOd are formed. not chromium hydroxide, proven. By sediment color (brown, not gray green), its composition determined by chemical (redox titration), atomic adsorption (spectrophotometer, C-302, flame analysis), {by potentiometric and potentiometric methods. j Example 1. The removal of hexavalent chromium ions from the prepared potassium dichromate solution containing 294.0 mg (0.01 MJ K CrjOy using sodium thiosulfate reducing agent is carried out. 159 mg of 0.01 M H2S04 is added to the initial solution and 55.21 mg 0.01 M On 8.0-5. This amount of reducing agent is necessary to reduce 50% of hexavalent chromium ions in solution. OD is added to NaOH with NaOH to achieve different pH values. The hydroxychromochlorine complex formed is filtered off under vacuum Bunsen flasks and a thief Büchner onks. The concentration of hexavalent chromium ions in the mother liquor is determined by bulk and photocolorimetric methods. Example 2, VO, 01 M potassium dichromate containing 294.0 mg K2Cr, jO-js add 219.9 mg of hydrazine sulfate. This amount of reducing agent is necessary to restore 50% of chromium ions (U1) in solution. OD is added to NaOH solution with NaOH to achieve different pH values. The remaining operations are similar to Example 1. The data obtained as a result of conducting experiments on the effect of pH and ratio Cr Cr presented in Table. 1 and 2.. Kz tab. It can be seen that the residual concentrations of hexavalent chromium in aqueous solutions are minimal during the treatment with pK 5 ,.

The results of experiments on the effect of the ratio of Cgb J cr on the residual content of ions are presented in ca.2.

From the data of Table 2 it follows that the maximum degree of wastewater recovery is observed at a ratio of 1: 1 and is 0.1 mg /

According to the proposed and known method, the initial ion concentration is 1040 mg / l, the residual ion concentration is 0.1 mg / l, the final pH value is 7.0 and sodium thiosulfate is taken as a reducing agent. With

Thus, the filterability of the precipitate by the proposed method is 1.32 "/ mch, and by the known 0, 184 M / MV4.

The technical and economic advantages of the proposed method consist in reducing the residual content of chromium ions in water, improving the filtration conditions of the sludge and obtaining a more dense sludge with a higher sedimentation rate.

The proposed method allows to reduce the consumption of reducing agents by 50%.

Table 1

Sodium thiosulfate

Hydrazine sulfate

Note. Initial concentration of Cg in ob16, 3 0.3 0.1 4.1

13.9 0.1 0.2 0.8 The solution being treated is 1040 mg / l

table 2

Claims (1)

METHOD FOR WASTE WATER CLEANING FROM IONS OF HEXVALENT CHROME, including treatment with a reducing agent, precipitation and separation of sludge, characterized in that; in order to reduce the residual content of hexavalent chromium ions in water, increase the filterability of the precipitate and reduce the consumption of reducing agent, the reducing agent is treated to an equal ratio of hexavalent and trivalent chromium ions in the water to be purified, and precipitation is carried out at pH 6.0-7.0.