RU2488439C1 - Method of producing lead sulphide-based composite sorbent - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to techniques of producing sorbents for extracting silver from waste water and process solutions. The sorbent is obtained using a dispersion of fibrillated cellulose fibres as lead sulphide carriers. Lead sulphide is precipitated with sodium sulphide in an aqueous dispersion which contains lead acetate or nitrate and said fibres. A sorbent containing 50-300 pts.wt lead sulphide per 100 pts.wt fibre is obtained.

EFFECT: invention enables to obtain a sorbent with capacity of 300-675 mg silver per 1 g sorbent.

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Description

The invention relates to technologies for producing sorbents for the extraction of silver by ion exchange from wastewater and technological solutions.

A known method of preparing a composite sorbent based on lead sulfide (SU, N1321681, C02F 1/58, publ. 07/07/87), including the preparation of inert carrier particles, which take sifted glass chips with a diameter of 0.5-3.0 mm or glass wool , by degreasing them using a chromium mixture, washing with soda solution and distilled water, preparing reagent solutions - potassium hydroxide, lead acetate, containing thiourea or thiosemicarbazide sulfur, mixing carrier particles in the mixer with these solutions and water to obtain dispersion of the particles in the reaction mixture. As a result of the reactions, chemical precipitation of lead sulfide occurs in it with its simultaneous mechanical immobilization on the surface of the carrier particles with the formation of a dispersion of composite sorbent particles. Next, the sorbent is separated from the water by filtration, washed with distilled water and dried. The carrier particles are coated with a lead sulfide film 30–50 nm thick. The specific surface area of the sorbent on glass wool is more than 1700 m ² / g, and its silver capacity is 0.3 mEq / g (32.36 mg / g, or 3.24% based on the weight of the sorbent).

This method of producing a sorbent based on lead sulfide can be considered a close analogue of the proposed method.

In processes for extracting silver from water, a known sorbent is used as a load in column type filters. In the example of use, the water treatment rate is 10 ml in 8.3 minutes per 5 cm ³ of the sorbent volume with the full consumption of its capacity.

The disadvantages of the method are the high complexity of its implementation, the long duration of the process, the low specific capacity of the resulting sorbent for silver, the long duration of the process of extracting silver from water when using this sorbent.

New results when using the proposed method are to simplify the process of obtaining the sorbent, increase its capacity, providing the ability to process water with a sorbent at a high speed equal, for example, to the rate of formation of a stream of water to be treated.

These results are achieved by the fact that in the method for producing a composite sorbent based on lead sulfide using an aqueous dispersion of inert particles as carriers of lead sulfide, as well as reagents from the series including lead acetate and a sulfur-containing reagent, which form one chemically different reagent in an aqueous medium precipitated lead sulfide, including the preparation of aqueous reagent solutions, processing a solution of one reagent with a solution of another in the presence of inert particles in an aqueous medium with by calling a composite sorbent in the form of carrier particles with lead sulfide immobilized on them, separating them from the aqueous medium, according to the invention, fibrillated cellulose fibers containing, in wt.%, at least 94% fibers with a length of not more than 1, are used as inert particles 23 mm and not less than 54% of fibers with a length of not more than 0.63 mm, a number of lead-containing substances additionally include lead nitrate, sodium sulfide is used as a sulfur-containing reagent, lead sulfide is immobilized on the fibers in chemical form during its chemical deposition de fine particles by the sorption mechanism, while the sorbent is obtained with a content of 50-300 wt.h. lead sulfide per 100 parts by weight fibers. The sorbent can be separated from the liquid phase by pressure flotation.

The method is as follows. An aqueous dispersion of fibrillated cellulose fibers (FCV) is prepared, containing, based on their weight, at least 94% of fibers with a length of not more than 1.23 mm and at least 54% of fibers with a length of not more than 0.63 mm, with a given fiber concentration in suspension, for example, in the range of 150-200 mg / DM ³ . Solutions of lead acetate or nitrate and sodium sulfide are also prepared. A predetermined amount of a PCV dispersion and a solution of a lead salt is fed into a flow mixer and a suspension of a PCV in a solution of this salt is obtained. Next, the suspension is sent to a flow reactor, to which Na ₂ S solution is also supplied in an amount stoichiometrically equal to the content of lead in the suspension. In the reactor, a reaction occurs between lead and sulfur ions, resulting in the formation of finely dispersed water-insoluble PbS particles. These particles in dispersion under the action of tensile forces are firmly immobilized on cellulose fibers, which are highly active in interacting with both newly formed particles and with each other.

The suspension is then fed to a saturator, where it is pressurized, for example, at 2 atm, saturated with air and sent to a water distributor in the flotator chamber. When the flow leaves the distributor, the pressure decreases to normal.

Due to its high activity, fibrillated cellulose fibers with PbS particles immobilized on them are capable of forming flocculi and flakes in the absence of mixing in 15-20 seconds. The structure and physical properties of the fibers and these formations contribute to the retention of air bubbles in them. Therefore, air bubbles released from the saturated water during depressurization flotate flocs and rapidly forming flakes to the surface of the water in the flotator well.

The accumulating layer of sludge, consisting of particles of a composite sorbent based on lead sulfide, is removed from the flotator and sent to a storage tank for subsequent use in processes for extracting silver from waste water or process streams.

Using this technology, it is possible to obtain a sorbent with a lead sulfide content in it in an amount, for example, from 50 to 600 parts by weight. per 100 parts by weight fiber. The value of this ratio upon receipt of the sorbent is chosen in accordance with the specific conditions of its use in water treatment. The preferred range of the ratio value (50-300): 100.

The following examples illustrate the proposed method.

Example 1. Prepare an aqueous dispersion of fibrillated wood cellulose fibers (FCV) containing, in wt.%, Not less than 94% of fibers with a length of not more than 1.23 mm and not less than 54% of fibers with a length of not more than 0.63 mm with a concentration 200 mg / dm ³ , a solution of lead acetate with a metal content of 86.6 mg / dm ³ , a solution of Na ₂ S with a concentration of 32.44 mg / dm ³ . First, the PCV dispersion and the lead acetate solution are mixed, and then a Na ₂ S solution is fed into the mixture at the same volumetric flow rates of the dispersion and solutions. As a result of chemical reactions in the dispersion, insoluble PbS particles are formed, which are immobilized on the PCV with the formation of a composite sorbent. Get, for example, 3 DM ³ suspension of the sorbent with its content of 300 mg and a concentration of 100 mg / DM ³ and a mass ratio of PbS: CV equal to 50: 100. The suspension is saturated at an air pressure of 2 atm, fed to a flotator, flotation sludge with a concentration of solids, for example, 3 g / dm ³ , is taken and taken to a tank.

Example 2. In contrast to the conditions of example 1, use a PCV dispersion with a concentration of 150 mg / dm ³ , a solution of Pb (NO ₃ ) ₂ with a lead concentration of 390 mg / dm ³ , a Na ₂ S solution with a concentration of 146.76 mg / dm ³ . Get 3 DM ³ suspension of the sorbent with its content of 600 mg and a concentration of 200 mg / DM ³ and a mass ratio of PbS: CV equal to 300: 100.

Example 3. In contrast to the conditions of example 1, the lead content in the solution is 260 mg / dm ³ , the concentration of N ₂ S is 97.84 mg / dm ³ . Get a suspension of sorbent with a concentration of 166.6 mg / DM ³ and the ratio of PbS: CV = 175: 100.

Sorbent can be used to extract silver from wastewater and process water. In the process of extracting silver from water, the sorbent is fed into it in the form of a slurry, which is dispersed to form an aqueous suspension with a high degree of dispersion of its particles. In this case, the important advantages of the proposed sorbent are used. When dispersing the flocculent sludge in water by mixing, the flakes and flocculi are easily and completely destroyed. However, when mixing ceases, flocculi and flakes re-form with high speed and easily float. This makes it possible to use the sorbent in silver recovery processes, including the use of flotation.

The capacity of the sorbents according to examples with respect to silver ions is 303, 751 and 540 mg per 1 g of sorbent.

Claims (1)

A method for producing a composite sorbent containing lead sulfide on fibers of a cellulose carrier, comprising mixing a solution of acetate or lead nitrate with a solution of sodium sulfide in the presence of fibrillated cellulose fibers in an aqueous dispersion containing in wt.% At least 94% fibers with a length of not more than 1.23 mm and not less than 54% of fibers with a length of not more than 0.63 mm, carried out for the deposition of lead sulfide and its immobilization in an amount of 50-300 parts by weight per 100 parts by weight said fibers, subsequent saturation of the resulting suspension with air under pressure and separation of the sorbent by pressure flotation.