RU2176617C1 - Method of purifying sewage from heavy metals - Google Patents

Abstract

FIELD: purification of sewage from heavy metals. SUBSTANCE: method comprises filtering sewage containing heavy metals through layer of sorbent which is essentially finely divided bark part of bark of coniferous species of wood exposed to extraction with hot water at certain temperature and flow rate. Method is efficient since sorption ability of used sorbent is higher as compared with other similar natural lignocarbohydrate materials. Sorption product is utilized by combustion. EFFECT: more efficient purification method. 2 tbl

Description

 The invention relates to the field of sorption wastewater treatment / SV / from the heavy metals contained in them / TM / and can be used at enterprises of machine-building, radio engineering, electronic and other industries, including having workshops and plots of electroplating.

Electroplating is widespread. Nickel plating, chromium plating, zinc plating, and some others are used as its main processes. Ions and TM compounds pose a serious danger to living organisms, especially humans, and Sch ⁶⁺ and Ni ²⁺ are among the most dangerous ions.

 Known sorption purification of CB from TM. In particular, when using ion-exchange resins, the technology is complicated and requires expensive and scarce materials. In this case, the problem of eluates formed during the regeneration of ion exchangers has not been solved, since a large amount of salts is dumped with them, which is harmful to the environment / 1 /. The problem of disposal of ion-exchange synthetic resins, which have lost their initial exchange capacity over time, is also not resolved, which leads to environmental pollution.

Known for the cleaning of CB from HM using chemically modified sorbents from waste from the woodworking and pulp and paper industries - sawdust and sludge-lignin / 2 /. As you know, sawdust is a material of ligno-carbohydrate nature. The modification consists in keeping wood sawdust in a modifier reagent solution, which is a new synthesis product - heterocyclic nitrogen compounds or monoethanolamine derivatives, with a reagent: sorbent ratio of 1: 10-100 for 1-24 hours or by passing a modifier solution through a sorbent layer in a column . The SW was cleaned from HM by passing it through a layer of sorbent / sawdust / placed in a glass column with a diameter of 20 mm and a height of 100 mm. Dynamic cleaning by filtering a solution with a concentration of Sch ³⁺ 10 mg / l through a modified sorbent with a filter cycle duration of 20 h increased the degree of extraction to 83-94.5% versus 71% in the initial untreated sawdust, and the specific capacity of the modified sorbent increased to 0 , 37-0.49 g MF ³⁺ / 1 kg compared with 0.20 g MF ³⁺ / 1 kg of the original sawdust. The disadvantage of this technology is that for the modification of sawdust synthetic nitrogen-containing compounds are used, which are toxic substances that are constantly washed from the modified sorbent into treated effluents, which leads, on the one hand, to their secondary pollution by toxicants, alien to the flora and fauna of natural water bodies, and another - to the need for additional modification of the sorbent. In addition, according to the data presented, the specific sorption capacity remains low / 0.37-0.49 g Sch ³⁺ per 1 kg of modified sorbent /, and the degree of purification is insufficient: under optimal conditions, it is 94.5%, which means that at the initial concentration of Sch ³⁺ 10 mg / l after purification, the residual concentration of Sch ³⁺ will be 0.55 mg / l, which exceeds the MPC.

 Thus, the known cleaning technologies have either limited application or low efficiency, but in general they do not solve the basic environmental, technical and economic issues of TM waste treatment / the production of ion exchange resins is environmentally "dirty", and their disposal has not been resolved /. The sorption capacity of modified sawdust is low, the degree of purification of CB from HM is insufficient, which leads to contamination of surface waters of HM.

The closest technology is the purification of CB from HM using coniferous bark / 3 /, which is a natural ligno-carbohydrate material. The cleaning is carried out in dynamic mode, passing the SW at a speed of 1 m / h through a glass column with a diameter of 20 mm and a height of 100 mm, filled with bark with a particle size of 1-5 mm. The degree of purification of CBs containing separately Ni ²⁺ , Fe ³⁺ , Sch ³⁺ , Sch ⁶⁺ , at a concentration of 5 mg / L of each ion with a 6-hour filter cycle was 72.0%, 32.0%, 78.1%, respectively and 57.4%. This means that after purification, CBs contained Ni ²⁺ 1.4 mg / L, Fe ³⁺ 3.4 mg / L, Mn ³⁺ 1.1 mg / L and Mn ⁶⁺ 2.13 mg / L, t. e. in all CBs, the ion concentration exceeded several times the MPC. Therefore, all these CBs required additional purification, did not meet sanitary and hygienic standards, and posed a threat to the environment. The specific sorption capacity at the optimum pH of 5 was: nickel 0.21 g / 1 kg of bark / 0.21 mg / 1 g of bark /, iron 0.24 g / 1 kg of bark / 0.24 mg / 1 g of bark /, chromium 1.12 g / 1 kg of bark / 1.12 mg / 1 g of bark /. In addition, the coniferous bark contains a significant amount of water-soluble substances, which leads to secondary contamination of the purified SW. Thus, neither in terms of the degree of purification of CB, nor in sorption capacity, nor in secondary pollution of treated effluents, bark can be recognized as an acceptable sorbent, despite its practically unlimited resources.

The technical problem solved by the invention consists in the purification of effluents containing HM, primarily Sch ⁶⁺ and N ²⁺ , to MPC standards and increasing the specific sorption capacity of the sorbent. The solution to the technical problem is achieved by the fact that as the sorbent use the cortical part of the coniferous bark, subjected to grinding and extraction with hot water, and the effluent is cleaned at a temperature of 25-38 ^o C and a filtration rate of 0.2-0.35 m / h. The study of the existing level of technology in this field on patent and scientific and technical sources of information showed that the proposed method, both in terms of sorbent and cleaning mode, differs from the known ones. The high efficiency of the proposed technical solution is due to the high sorption capacity of the sorbent, which distinguishes it from similar ligno-carbohydrate materials, and the ability to clean CB with both low and high / hundreds of mg / l / concentration of HM. Particularly effective the proposed method for the treatment of effluents from compounds Sch ⁶⁺ , because it does not have the stage of preliminary reduction of Sch ⁶⁺ to Sch ³⁺ , which is the most expensive operation in the entire system of purification from the specified ion. With a high sorption capacity, the availability of the sorbent is ensured by a wide raw material base - large-tonnage waste from debarking coniferous wood. Sorption products can be disposed of by incineration, where the sorbent itself acts as fuel. The obtained TM oxides can be used in various directions, in particular as a highly refined ore raw material / the content of chromium oxide-Сч ₂ O ₃ - in the ash residue is 70% or more, and nickel - 30% or more /.

 The sorbent was obtained from the cortical part of the bark of spruce and pine / waste debarked wood processing enterprises of Karelia / by grinding and extraction with hot water to remove water-soluble components. The sorption process was carried out in a dynamic mode by passing a CB through a sorbent placed in a glass column with an inner diameter of 40 mm and a length of 500 mm. The ratio of the diameter of the sorbent column to its height is 1: 4-5. The purified water was filtered in the direction from top to bottom, adjusting the flow rate. CB was obtained by diluting spent and working solutions of nickel and chromium plating at enterprises in Petrozavodsk.

 The proposed method is illustrated by 15 examples.

Example 1. A sorbent was loaded into a glass column with an inner diameter of 40 mm and a height of 500 mm so that its height was 170 mm. By diluting the spent solution, a CB with a concentration of Ni ^{2+ of} 85.0 mg / L was obtained, which was heated to a temperature of 38 ^° C and filtered through a sorbent bed at a speed of 0.23 m / h. The cleaning cycle was 4.5 hours. Ni ²⁺ ions were absent in the filtrate, the filtrate was stained and the COD was 120 mg O ₂ / L / purification data are given in table. 1/.

Example 2. A column with a sorbent and a CB solution were prepared as in Example 1, but the CB was heated to a temperature of 41 ^° C and filtered at a speed of 0.21 m / h. The duration of the cycle was 4 hours 40 minutes. In the filtrate, the concentration of Ni ²⁺ was 1.1 mg / L, which is higher than the MPC. The filtrate was intensely stained and COD was 253 mg O ₂ / L / purification data are given in table. 1/.

Example 3. A column with a sorbent was prepared as in Example 1. By diluting the working solution from a nickel bath, a CB with a Ni concentration of ² + 77.4 mg / L was obtained. CB was heated to 25 ^o C and filtered through a layer of sorbent at a speed of 0.20 m / h The cycle time was 4 hours 20 minutes. There was no Ni ²⁺ ion in the filtrate, i.e. the degree of purification was 100% / data on cleaning are given in table. 1/.

Example 4. A column with a sorbent was prepared as in Example 1. By diluting the working solution from a nickel plating bath, CB with a Ni ²⁺ concentration of 77.4 mg / L was obtained. SW with a temperature of 21 ^o C was filtered through a layer of sorbent at a speed of 0.20 m / h Cycle time 4 h 40 min. In the filtrate, the concentration of Ni ²⁺ was 2.3 mg / L, the degree of purification was 97.1% / data on the purification are given in table. 1/.

Example 5. A sorbent was loaded into a glass column so that its height was 200 mm. Wastewater with a concentration of Ni ^{2+ of} 8.6 mg / L was obtained by diluting the spent nickel solution. CB was heated to 28 ^° C and filtered through a sorbent at a speed of 0.35 m / h. The cycle time was 3 hours 30 minutes. There was no Ni ²⁺ ion in the filtrate, the degree of purification was 100% / purification data are given in table. 1/.

Example 6. A column with a sorbent was prepared as in example 5. CB with a Ni ²⁺ concentration of 7.5 mg / L was prepared as in example 5. CB was heated to a temperature of 29 ^° C and filtered at a speed of 0.38 m / h. The cycle time was 3 hours 45 minutes. In the filtrate, the concentration of Ni ²⁺ was 1.3 mg / l, the degree of purification 82.6% / data on cleaning are shown in table. 1/.

Example 7. A column with a sorbent was prepared as in example 1. CB with a Ni ²⁺ concentration of 74.8 mg / L was obtained as in example 1. CB was heated to a temperature of 25 ^° C and filtered at a speed of 0.17 m / h. The cycle time was 5 hours 15 minutes. The Ni ^{2+ ion was} absent in the filtrate, but the solution was stained and COD was 130 mg O ₂ / L / purification data are given in Table. 1/.

Example 8. A column with a sorbent was prepared as in Example 1. As CB, artesian water with a concentration of Fe ^{3+ of} 5.2 mg / L was used. CB was heated to 27 ^o C and filtration through the sorbent was carried out at a speed of 0.22 m / h. The cycle time was 4 hours 30 minutes. In the filtrate, the concentration of Fe ³⁺ was 0.43 mg / L, the degree of purification was 94.8% / the data on purification are given in table. 1/.

Example 9. A glass column with an inner diameter of 40 mm and a height of 500 mm was loaded with a sorbent so that its height was 170 mm. CB was prepared by diluting the working solution from the chromium bath to a concentration of Sch ⁶⁺ 45.6 mg / L, Sch ³⁺ 0.4 mg / L / Sch _total - Sch ⁶⁺ in units. SCO ₃ /. CB was heated to a temperature of 34 ^° C and filtered through a sorbent at a speed of 0.21 m / h for 4 hours and 45 minutes. In the filtrate, the residual concentration of Sch ⁶⁺ was 0.04 mg / L, Sch ³⁺ 0.19 mg / L, and Sch _total 0.23 mg / L. The degree of purification according to Sch ⁶⁺ was 99.9%, the filtrate met the requirements of the MPC according to Sch ⁶⁺ and Sch ³⁺ / the cleaning data are given in table. 2 /.

Example 10. A column with a sorbent and CB was prepared, as in example 9. CB was heated to a temperature of 26 ^o C and filtered at a speed of 0.27 m / h for 4 hours. In the filtrate, the concentration of Sch ⁶⁺ was 0.04 mg / l , Sch ³⁺ 0.21 mg / L, Sch _total 0.25 mg / L / all concentrations are given in units. SCO ₃ /. The degree of purification according to Sch ⁶⁺ is 99.9%. According to the content of MF ⁶⁺ and MF ^{3+, the} filtrate corresponded to the MPC requirements / cleaning data are given in table. 2 /.

Example 11. A column with a sorbent was prepared as in example 9. CB was obtained by diluting the working solution from the chromium bath to a concentration of Sch ⁶⁺ 46.0 mg / L, Sch ³⁺ 0.6 mg / L. SW with a temperature of 22 ^o C was filtered through a sorbent at a speed of 0.20 m / h for 5 hours. In the filtrate, the concentration of Sch ⁶⁺ was 0.20 mg / L, Sch ³⁺ 0.38 mg / L, Sch _total 0, 58 mg / l / all concentrations are given in units. SCO ₃ /. SV after cleaning did not meet the requirements of MPC / data on cleaning are given in table. 2 /.

Example 12. A column with a sorbent was prepared, as in example 9. CB was obtained by diluting the working solution from the chromium bath to a concentration of Sch ⁶⁺ 45.0 mg / L, Sch ³⁺ 0.6 mg / L, Sch _total 45, 6 mg / l / all concentrations are given in units. SCO ₃ /. CB was heated to 32 ^o C and filtered through a sorbent at a speed of 0.37 m / h for 3 hours. In the filtrate, the concentration of Sch ⁶⁺ was 0.48 mg / L, Sch ³⁺ 0.14 mg / L, Sch _total 0 , 62 mg / l. SV after cleaning did not meet the requirements of MPC / data on cleaning are given in table. 2 /.

Example 13. A glass column with an inner diameter of 40 mm and a length of 500 mm was loaded with a sorbent, so that its height was 210 mm CB was prepared by diluting the spent chromium solution to a concentration of Sch ⁶⁺ 268.4 mg / L, Sch ³⁺ 3.9 mg / L, Sch _total 272.3 mg / L / all concentrations are given in units. SCO ₃ /. CB was heated to 29 ^° C and filtered through a sorbent at a speed of 0.18 m / h for 5 hours and 20 minutes. The concentration in SW Mn ⁶⁺ was 0.25 mg / L, Mn ³⁺ 1.03 mg / L, Mn _total 1.28 mg / L, i.e. the concentration of Sch ⁶⁺ and Sch ³⁺ exceeded the MPC requirements / cleaning data are given in table. 2 /.

Example 14. A column with a sorbent and CB was prepared as in Example 13. CB was heated to 30 ^° C and filtered through a sorbent at a speed of 0.16 m / h for 5 hours and 30 minutes. In the filtrate, Sch ^{6+ was} absent, Sch ³⁺ concentration was 0.48 mg / L, Sch _total 0.48 mg / L. The filtrate met the requirements of the MPC, although it was stained by dissolving the sorbent substances / cleaning data are given in table. 2 /.

Example 15. A column with a sorbent was prepared as in example 13. CB was obtained by diluting the spent chromium solution to a concentration of Sch ⁶⁺ 209.0 mg / L, Sch ³⁺ 3.7 mg / L, Sch _total 212.7 mg / l / all concentrations are given in units. SCO ₃ /. CB was heated to 29 ^° C and filtered through a sorbent at a speed of 0.20 m / h for 5 hours. There was no Sch ⁶⁺ in the filtrate, the concentration of Sch ³⁺ was 0.34 mg / L, Sch _total 0.34 mg / L , i.e. the degree of purification met the requirements of the CDK / data on purification are given in table. 2 /.

According to "Appendix 2""Sanitary rules and standards for the protection of surface water from pollution". Ed. official M. - 1988. - 70 s., Introduced from 01.01.1989, MPC values for nickel 0.1 mg / l, Mn ⁶⁺ 0.05 mg / l, Mn ³⁺ 0.5 mg / l / NN for / p in "Appendix 2" 815, 1265 and 1264 /.

From the above table. 1 and 2 of the data it follows that the optimal parameters of the proposed method of sorption purification are the temperature of 25 - 38 ^o C and the filtration / flow rate / 0.20 - 0.35 m / h When the SV temperature is increased to 41 ^° C, the filtrate contains 1.1 mg / L Ni ²⁺ , which significantly exceeds the MPC value, and has an increased amount of sorbent substances / Example 2, table. 1 /. When lowering the temperature of the cleaned CB to 21 ^o C / example 4, table. 1 / and up to 22 ^o C / example 11, table. 2 / the concentration of Ni ²⁺ and Sch ⁶⁺ is 2.30 mg / L and 0.20 mg / L, respectively, which significantly exceeds the MPC requirements for these ions. With an increase in the rate of flow of SW through the sorbent to 0.33 m / h / example 6, table. 1 / and 0.37 m / h / example 12, table. 2 / the concentration of Ni ²⁺ and Sch ⁶⁺ was 1.3, mg / L and 0.48 mg / L, respectively, which significantly exceeds the MPC. At a high concentration of Sch ⁶⁺ / 268.4 mg / l /, a decrease in the filtration rate to 0.18 m / h does not lead to positive results / Example 13, table. 2 /. With a further decrease in the filtration rate to 0.17 m / h / example 7, table. 1 / and up to 0.16 m / h / example 14, table. 2 / the degree of purification meets the requirements of the MPC, but at the same time an increased amount of sorbent components passes into the filtrates, which increases the COD and the color of the purified CB. In addition, reducing the flow rate is impractical from an economic point of view. From the data table. 1 and 2 it follows that the sorbent in the proposed cleaning method has an incomparably greater sorption ability compared to the known / coniferous bark /: for one filtration cycle, its specific sorption is 0.23 - 3.4 mg Ni ²⁺ / 1 g of sorbent and 1.68 - 7.71 mg Cf ⁶⁺ / 1 g of sorbent, but a positive cleaning effect (up to the value of CDC) is achieved under certain conditions: temperature during cleaning 25 - 38 ^o C and flow / filtration rate / 0.2 - 0 , 35 m / h

According to repeated experiments with multiple cycles of CB purification through the same sorbent mass, sorption of Ni ²⁺ reaches ^9–12 mg / 1 g of sorbent, and Sch ⁶⁺ 200 - 230 mg / 1 g of sorbent. From the patent and other sources of scientific and technical information, natural ligno-carbohydrate sorbents with a similar sorption capacity are unknown. In addition, sorption of Sch ⁶⁺ , as follows from the above data, took place without transfer to Sch ³⁺ , i.e. there was direct sorption of this important technological agent and the most dangerous toxicant. The proposed sorption purification allows the implementation of a process that meets environmental requirements, without the use of different types of equipment. The sorption product can be disposed of in several ways.

 An unlimited raw material base for the production of sorbent, simple operations to obtain a sorbent, and the simplicity of the waste water purification process from HM in a wide range of their concentrations without any significant costs for chemicals, electricity, water and equipment - all this allows us to consider the proposed sorption treatment as industrially applicable.

Sources of information
1. Grebenyuk V.D., Sobolevskaya T.T., Makhno A.G. Status and development prospects of wastewater treatment methods of galvanic production // Chemistry and water technology. - 1989.- T. 11, N 5. - S. 407 - 421.

 2. Timofeeva S. S., Lykova O. V., Kukharev B. F. The use of chemically modified sorbents for the extraction of metals from wastewater // Chemistry and technology of water. - 1990. - T. 12, N 6. - S. 505 - 508.

 3. Timofeeva S. S., Lykova O. V. Sorption extraction of metals from wastewater of galvanic production // Chemistry and technology of water. - 1990. - T. 12, N 5. - S. 440 - 443.

Claims (1)

A method of treating wastewater from heavy metals, including filtering through a sorbent layer of ligno-carbohydrate nature, containing crushed bark of coniferous wood, characterized in that the cortical part of the coniferous bark pre-extracted with hot water is used as ligno-carbohydrate material, and cleaning is carried out at a temperature of 25- 38 ^o C and at a flow rate of 0.2-0.35 m / h

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