Method of regeneration of spent chrome tanning solutions

 

(57) Abstract:

The invention relates to methods for the regeneration of spent solutions containing toxic chromium compounds, for example, leather and fur industries. The essence of the method consists in the preliminary allocation balanced and fatty substances from waste solutions by settling and filtration, with subsequent introduction of a reagent - oxidant and heated to decomposition of dissolved organic impurities. Freed from organic impurities spent solution is mixed with fresh tanning agent and returned to the process. The proposed method allows to reuse the solutions of tanning agent without reducing product quality. 1 C.p. f-crystals.

The invention relates to methods for the regeneration of spent solutions containing toxic chromium compounds, for example, leather and fur industries. The difficulty of regeneration and purification of such solutions is that they are stable heterogeneous disperse system. Such solutions contain dissolved organic impurities, for example, a variety of amino acids, liquid and solid suspension, the remains of the dermis of the skin. Vtiger 2000-4000 mg/l, chromium compounds-2-6.3 g/l in terms of CR2ABOUT3organic impurities in terms of the amount of COD (chemical oxygen demand on the mineralization of the organic impurities to higher oxides) solutions 1700-11000 mg/l at pH 3.5-5. Up to 32% of the initial chromium reagents is lost with sewage and other wastes that pollute the environment.

The most common in the leather industry is a method of regeneration of chromium, consisting in the deposition of chromium alkalis (method of purification of sewage under tanneries. Leather Manuf. - 17, 1991, No. 2, s.7-8). The spent solution after tanning animal enters the settling tank for separation of fat and pop substances, hereinafter mesh filter for selection of leather or fur fibers and other solid particles. Freed from these impurities, the solution fed to the mixing with caustic soda and polymers. Under stirring for two hours to carry out the neutralization of acidic solutions to pH 7-9 with obtaining chromium hydroxide, which is separated and dewatered on a vacuum filter. The degree of extraction of chromium exceeds 95%. Dewatered sludge is treated with sulfuric acid for dissolving chromium hydroxide and return it to the stage is truemate sediment, the high cost of soda, polymer, sulfuric acid, a multi-stage process, the presence in the aqueous phase - wastewater compounds of chromium with a concentration substantially higher than the MPC.

There is a method of regeneration of spent tanning solutions, which consists in using at the stage of tanning mixtures of fresh tanning agent and 10-20% of spent tanning solutions (Use of spent tanning solutions for the production of leather for bottom shoes. Izvestiya Vuzov. The technology of light industry, 1990, V. 33, No. 4, S. 29-31). At this ratio, the spent solution and fresh tanning material quality tanning leather for bottom shoes meets the technical requirements. By increasing the content in the tanning solution share the spent solution from 20 to 40% decreases the utilization of chromium, quality decreases podobrannoj skin, but the content in the exhaust impurities of organic and mineral substances increases. The concentration of spent tanning solutions offer ultrafiltration.

The disadvantages of the method include: incomplete excretion of chromium compounds, low recycling solutions, the complexity of the selection components Riskin to claimed is a method of regeneration of spent solutions chrome tanning of leather manufacture (Russian Federation patent No. 2129992. Method of regeneration of spent solutions of chrome tanned leather production. Panov, B. N., Drying Agent A. C., B. I. No. 13, 10.05.99). The technical result is achieved by first conducting the allocation of fatty substances and solids by settling and filtration, the fine particles are separated by centrifugation to a residual content of not more than 150 mg/L. solution is mixed with a reagent (hydrogen peroxide in amounts of 10-150% of the stoichiometric amount in the calculation of the COD of the solution. Then the solution is treated with UV rays for 15-120 min when the irradiation intensity of 15-60 kW/m3and after reaching magnitude COD 300-800 mg/l direct mixing with fresh tanning agent while maintaining the tanning properties of waste solutions.

The proposed method eliminates the stage of deposition of chromium compounds from waste solutions. Almost completely excluded: wastewater generation, the cost of alkaline reagents for the precipitation of chromium and acids on the dissolution of chromium hydroxide. However, requires a selection of the fine particles by centrifugation, expended energy for the UV treatment of waste solutions.

Technical armaturnogo execution of the regeneration process waste solutions and the provision of such compositions of mortars, the use of which is at the stage of tanning leads to higher quality prodoljennyh skin.

The technical result is achieved by the fact that after separation of the fat and suspended solids by settling and filtration, the solution is mixed with hydrogen peroxide in amounts 15-50% of the required for complete mineralization of organic impurities in the calculation of the COD of waste solutions. After this, the solution is heated to 50-70C and maintained at this temperature 120-30 min until complete decomposition of the hydrogen peroxide. When this occurs the decomposition of organic impurities, the destruction of the stability of dispersed systems with the formation of the organic phase and the solution, which is separated by settling. In the regenerated solution of chromium compounds serves fresh technical tanning agent to achieve the technological concentration of chromium in the tanning of raw materials. In this way, the regeneration of spent solutions retained their tanning properties. Tanning of the hide, in this way improving the quality podobrannoj skin, for example, temperature increases welding 5-10C compared to the temperature of the welding of the skin, podobrannoj freshly prepared solution.

Example 1. The spent solution from the study mg/l at pH of 3.15. The solution was mixed with hydrogen peroxide at the rate of 5.3 g of N2ABOUT2g/l (calculated on the COD - 25% of the stoichiometric standards) and was heated to 50C. The mixture was stirred for 120 min, then spent the separation of the phases by settling. In the regenerated solution, the chromium content and pH remained unchanged, and the COD value was reduced to 576 mg/l in the absence of suspended solids, and the regenerated solution was injected into a fresh technical tanning agent to achieve the chromium concentration 12 g/l and the mixture was dobili sample of the hide, sheepskin. Pogublennaya skin had a positive test instrumentation, and the temperature of the welding rose to 110S against S in the fresh solution of the tanning agent.

Example 2. The spent solution is chrome tanned sheepskin, after sedimentation, filtration contain: chromium - 5.6 g/l, suspended solids 240 mg/l, COD - 850 mg/l at pH 3,22. To the solution was added hydrogen peroxide 2.7 g/l (calculated on the COD of the solution 15% of normal), the mixture was heated to 70 C and kept at this temperature for 60 minutes Defending divided phase in the aqueous phase of the chromium content and the pH has not changed. COD decreased to 315 mg/l In solution gave a fresh tanning agent to achieve the chromium content of 10 g/l and the mixture was probbaly sample of the hide, sheepskin. In podobrannoj skin test instrumentation polojitelinii goat after settling and filtering included: chrome - 3,90 g/l, suspended solids 150 mg/l, COD - 8640 mg/l at pH 3,70. After adding hydrogen peroxide to 9.2 g/l (calculated on COD 50% of normal), the mixture was heated to 70 C and kept for 30 minutes To separate by settling the aqueous phase of the chromium content and the pH has not changed, the value of COD was reduced to 260 mg/l In solution gave a fresh tanning agent to the chromium content of 10 g/l and the mixture was probbaly sample goat. Sample KIP podobrannoj skin positive temperature welding 115S against S outdoor tanning agent.

The experiments indicate achievement at specified parameters of the regeneration of spent tanning solutions that are acceptable for the process of tanning the content of organic impurities in them, the chromium content and the pH does not change. The regenerated solutions are suitable for the preparation of working tanning solutions with the introduction of fresh tanning material to the required technology to different types of tanning of the hide (cattle, sheepskin, goat and so on) contents of chromium. By the present method reduces energy costs, simplifies hardware design of the regeneration process, as it does not require centrifugation, is excluded from the technological scheme of regeneration solutions of the UV reactor CLASS="ptx2">

1. Method of regeneration of spent chrome tanning solutions, including the allocation of fat and suspended solids by settling and filtration, the mixture solution with hydrogen peroxide and return solution to tanning, characterized in that after the introduction of the hydrogen peroxide solution is heated and maintained until complete decomposition of hydrogen peroxide, after which the regenerated aqueous solution of a tanning agent is separated by settling, mixed with fresh tanning agent.

2. The method according to p. 1, characterized in that hydrogen peroxide is injected in quantities 15-50% of the stoichiometric standards for complete mineralization of the organic impurities in the calculation of the chemical oxygen demand of the solution, the mixture is heated to 50-70C and incubated for 30-120 minutes

 

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