CS258716B1 - A method of treating brine for electrolysis - Google Patents

Abstract

The solution relates to the chemical treatment of brine, which achieves the precipitation of unwanted ions, which are by-products of the table salt from which the brine is prepared. The precipitated substances are subsequently removed together with mechanical impurities. Barium compounds are used for precipitation, and the treatment is carried out in two stages, first in an acidic environment, and then in an alkaline environment. The solution according to the invention is suitable for the treatment of brine before electrolysis, in which caustic soda and chlorine are produced from it.

Description

258716

BACKGROUND OF THE INVENTION The present invention relates to the treatment of an aqueous solution of NaCl - brine for electrolysis to produce a chlorine and NaOH. The production of chlorine and NaOH by the electrolysis of brine is one of the oldest electrochemical products, and nowadays, inter-core production is included. In the course of the technology, it has been found that it is necessary to adjust the brine prior to the electrolysis so that some cations of metals such as Fe, Ca, Mg, Al and the like are removed from the solution. and also to adjust the concentration of the sulfate ionic level desired. This happens by the action of the agents, especially NaOH, Na 2 CO 3, CaCl 2 and BaCl 2. Alkali reagents with a sulfate ion precipitator are also known. a combination of Na 2 CO 3 and BaCO 3, wherein the resulting pH of the solution is in the alkaline range. In order to separate precipitated dirt particles, it is important that the precipitated substances are removed from the brine as completely as possible and that the precipitated particles are filtered well. In doing so, it is important that these requirements are met with a relatively low consumption of needed chemicals. In addition to the influence of the temperature, which is generally in the range of 60-70 ° C, it has been shown that the stated requirements are positively influenced and increased by alkalinity. These requirements are more time-consuming for recirculation of brine in the modern electrolysis process, whereby only the necessary technological amount is removed from the recirculated brine to prevent an increase in the concentration of undesirable substances at a natechnologically acceptable level. For better separation of precipitates, auxiliaries such as gelatin, agar-agar or flocculants such as polyacrylamide are added to the brine.

According to the invention, the electrolysis salt is treated by the action of barium salt precipitating agents and subsequent separation of the precipitated substances together with the mechanical impurities such that the treated brine solution, preferably by saturating the recirculated brine, is treated with pH below 6.5 by stirring with at least one barium compound in an amount of 0.7-1.1 moles of barium compounds, calculated on the sulphate present at 40-85 ° C, and after dissolution the system is made alkaline by treatment with NaOH after 0 5 to 4 hours after the addition of the precipitating agent, the solid phase is usually separated from the system by filtration. An advantage of the process of the invention is that it reduces the cost of precipitation of non-desirable ions from the brine, while a high separation of precipitated particles in a relatively short time is achieved and the treated salt has very good properties even in the process of electrolysis. especially in terms of current yields.

The term "brine" is intended to include the aqueous solution of chloride sodium chloride in the description of the invention, irrespective of its geological or chemical composition. geographic implementation, as it is obtained by mining or after its further modification. The brine described in the description is intended for electrolytic treatment into sodium hydroxide and chlorine. Typically, the concentration of sodium chloride in the prepared saline is in the range of 250 to 350 g / l, but these concentration limits are not limited. For the preparation of brine, it is expedient to use recirculated waste electrolysis waste, which is added to the kitchen prior to careful technological use, when it is usually drained before it is saturated, so as to avoid undesirable build-up of impurities.

The kitchen salt used in the preparation of the brine is neither a physical nor a chemical substance, but it contains mechanical impurities as well as chemically different substances which need to be removed therefrom prior to electrolysis, or their concentration can be adjusted to a technologically permissible concentration level. In the process of the invention, this treatment is carried out by precipitation and subsequent separation of the solid phase. It has been shown that by using barium compounds such as barium chloride, barium hydroxide, barium carbonate, a remarkable reduction in the consumption of these auxiliary chemicals can be achieved if the precipitation occurs firstly in the acidic environment formed by the presence of acidic salt and only after the distribution, if the reaction of the treated brine is transferred to the alkali region. For this purpose, I can use either individual barium compounds, or combine together. Their dosage is usually carried out in a slurry form, with the brine phase being the liquid phase. The blending agent, when added with the added reagent, is blown through with air or other inert gas, but can also be solved by using mechanical stirrers. The amount added is calculated from the amount of dissolved sulphates in the brine, taking into account their desired final concentration.

After mixing the precipitating agent in the brine, the system is made alkaline with NaOH and / or carbonate, the resulting pH being preferably 10.

After the appropriate time, usually 0.5 to 4 h, the solid phase is separated from the system, most often by filtration, using hydrocyclones, or by simple sedimentation in conical bottom containers. The saline thus prepared is either fed directly to the electrolysis or stored in containers.

The process according to the invention can conveniently be combined with some other known measures such as the use of flocculants, the use of agglomerating agents or the combination of alkaline agents.

Specific embodiments of the invention will be illustrated by the following examples.

Claims (2)

Example 1 For the electrolysis, the solanate salt is recycled to a NaCl concentration of 300 g / l. The aquaculture feedstock is used by Artemian salt from the USSR. Analysis of the salt used is as follows: insoluble residue 0.08 wt. R3O3 0.023 wt. CaO 0.293 wt. MgO 0.034 wt. % CaSO4 0.588 wt. humidity 0.030 wt. NaCl 98.95 wt. Technical hydrochloric acid was added to the saturated solution after heating to 70 ° C so that the resulting solution had a concentration of C - 0.07 mol of HCl / l solution. After this treatment, the precipitating agent is added as a suspension of BaCl 2 and BaCO 3 in a ratio of 3: 7 in a total amount of 25% by weight in brine (NaCl). The reagent is added in a molar ratio so that the concentration of sulfate ions remains in the amount corresponding to 3 g of Na 2 SO 4 / l after precipitation. After homogenization, the resulting system is made alkaline with NaOH and Na 2 CO 3 to pH 10, while stirring is effected by blowing through the air. The solid phase from this system is completely removed by filtration. The obtained filtrate contains 3 g of Na 3 SO 4/1 sulfate ions and the use of electrolysis reduces the formation of solid amalgam. Example 2 For a model test of the efficiency of the brine treatment, a solution containing 300 g / l NaCl pa and 0.01056 g SO42 / ml is prepared. We digest with HCl to pH 4.9. After adjusting the pH, add an equivalent amount of Ba (OH) 2.8 H2O to precipitate 1/3 of the sulphates present. The solution was heated under a reflux condenser at 70 ° C for half an hour. After heating, the un-precipitated sulfurates, calculated as the amount of solution C = - 0.1 mol / l Ba.Cl2, are determined and its excess is complexometrically determined. The determined sulphate precipitates are 120% of the theoretical amount (double-salt formation is assumed). The experiment demonstrates a reduction in the precipitating agent consumption to the desired reduction in consumption. SO4 2 by 20 wt. After adjusting the pH to the aical zone and separating the solid phase, the brine can be used for electrolysis. P RED m E τ The brine treatment method for electrolytic treatment of solibarium-based coagulating agents and the subsequent separation of precipitated precipitates together with mechanical impurities, characterized in that the treated brine solution is preferably treated at a pH below 6 by saturating the recirculated feed 5 with stirring at least one barium compound in an amount of 0.7-1.1 moles of barium compounds, calculated on the sulphate ions present, at 40-85 ° C, and after dissolution the system is basified with NaOH after From 0.5 to 4 hours after the addition of the precipitating agent, the solid phase is separated from the system by filtration.