SU802195A1 - Method of waste water purification from hexavalent chromium compounds - Google Patents

Description

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The invention relates to electrochemical processes and can be used to purify hexavalent chlorine compounds from waste waters that do not contain free acids and with low concentrations of dissolved salts from impurities.

The known method of electrocoagulation cleaning with soluble iron (steel) anodes formed during etching and passivation of non-ferrous metal products and in the electroplating industry of washing water with a content up to .120 mg / l C g (VI held at current densities up to 0.8-1 , 2 A / dm and the distance between the electrodes is 30-50 mm 1.

The closest technical solution to the invention is the method of wastewater treatment by electrocoagulation with soluble steel anodes with a relatively high concentration of free acids (pH up to 2-3) and dissolved salts (from several hundred mg / l to 1-1.5 g / l) at current densities of the order of 1 A / dm and usual (room) temperature with neutralization, if necessary, of excess acidity of the medium with alkaline chemicals after electrolysis

and settling (within 2 hours) of precipitation.

However, the known electrolysis modes are not applicable for the purification of chromium (VI) wastewater that does not contain free acids and with low concentrations of dissolved salts, due to the formation of

0 anions (50, CG, etc.) of viscous amorphous oggshkov chromium and iron hydroxides in their passivation of the surface of iron anodes, poor settling and filterability of water mist 5 from the treated effluent, as well as high electrical resistance of solutions and, consequently, greater specific electric power consumption to clean up. Besides,

0 for the implementation of the process requires a significant amount of neutralizing reagents, which increases the cost of cleaning.

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The aim of the invention is to increase the degree of purification, reduce energy consumption and implement the purification of waste waters that do not contain free acids and with low concentrations.

0 dissolved salts.

The assigned target is achieved by the J.1 current carried out in the electrolyzer, JTO type with steel growth iodine with a maximum of 11 electrodes, temperature preferably at 70 Ji current capacity at the anodes 3 A / DM, preferably A / dm.

Lovish temperature enhances the coagulation of hydroxide precipitates and contributes to the formation of instead of rykh and: dehydrated more dehydrated chris; but lichasnye suspensions, better settled, oh, because of the force of gravity and better than glutants. filter; weakened:. ::: g: the adhesion of surfaces with the surface:; removing them from the anodes; reduces the floor ;; ,:, 1a.ation of the process of dissolving the anodes and increasing the current efficiency of iron (I) slining. Electrical resistance ::; khochnaya WATER, intensifies the process of chromium (VI) iron termination And increases the degree of chromium purification and utilization, gland.

Below, the positive effect of temperature is weakened, upper g: the limit is limited by the boiling water.

The establishment of current densities in int 0zal / 0-0-0.3 L / dm is due to the prevalence of maintenance and reception, as well; 13; 13 production practices: PC -: limits, as well as ensuring good working conditions .- 11 fruits and iron dissolving with high current output under conditions of processing: - st; and drains with negligible content of acid anions in their composition.

The use of a current density below 0., 05 A / dm is impractical because of a decrease in the performance of the electroj.;: I; spa, In the current density range of 0, :) 5.0j3 A / dm, no passivation of the electrodes is observed while the iron current is maintained ( P) at a level of 9b, 5-100%, and at current densities of 0.3 A / dm, passivation, anode, and a decrease in current efficiency are observed.

In addition, the use of the proposed electrolysis mode allows reducing the total salt content of water by 35-50% compared to lo-15% at room temperature, which allows the use of purified distillate as desalinated water, and, in particular, bichromate condensate production as feed water KOTLOVOY.

Example. Source condensate containing, mg / l: 48.8 C g (VI),

0.5 Fe; 25 S02-; 9.9 С -; 0.3 Ca; 0.4 MD and having a pH of 6, was subjected to electrocoagulation purification in a laboratory electrolysis of continuous action with steel electrodes at a current density of 0.1 A / dm, temperature in the interelectrode distance of 10 mm.

The current efficiency of the anodic reaction Fe-2e- Fe (i) was 96.5%, the capacity of the electrolyzer was 3.9 l / h with the working surface of the anodes 3.5 dm, the consumption of iron for the reduction was 4.5 parts by weight on 1 weight. Cr (vi). The voltage on the electrolyzer is 4.8 V. The specific energy consumption is 21.5 kWh / kg Cg (VI).

The chromium and iron hydroxides formed with suspension were separated by filtration on a filter with a cloth at a speed of 0.25 m.

The purified condensate is transparent, without the presence of Cg (VI) (the degree of purification from Cg (VI) is 100%) with a pH of 8.5.

The final concentration of impurities, mg / l: Fe 0.1; Ca 0.1; Md 0.2; decrease in total salt content during purification of 35%. In terms of the residual salt content of free alkalinity and other limited impurities, the condensate met the requirements for feedwater of steam boilers.

Using this method allows you to achieve complete cleaning of chromium effluent using purified effluent in the process cycle.

Claims (2)

1. Non-ferrous metals, No. 4, 1974, p. 85-86. 2.Archakova G.A. Electrocoagulation method for purification of chromium-containing Wastewater. On Sat Issues of water management, Minsk, 1974 (prototype).