RU2850613C1 - Method for obtaining iron-containing coagulant from pyrite slag - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to inorganic substances technology and can be used in the production of iron sulphate and chloride solutions used as coagulants for wastewater treatment. The method for producing an iron-containing coagulant includes treating sulphuric acid production waste - pyrite cinders - with solutions of sulphuric acid at a concentration of 30-40% or hydrochloric acid at a concentration of 15 to 20%. The ratio of sulphuric acid production waste to acid reagent is 1:3.6 g/ml.

EFFECT: increased efficiency of wastewater treatment and utilization of sulfuric acid production waste.

1 cl, 3 dwg, 3 tbl, 28 ex

Description

The invention relates to the technology of inorganic substances and can be used in the production of solutions of ferric sulfate and chloride, used as a coagulant for wastewater treatment.

A known method for producing an iron-containing coagulant from scale (RU Patent No. 2759099, published November 9, 2021) involves treating the scale with a chlorine-containing reagent, wherein the chlorine-containing reagent is a mixture of 10-38 wt.% hydrochloric acid with the addition of 5-20 vol.% titanium tetrachloride. The ratio of the mass of scale to the volume of the chlorine-containing reagent is 1:(5-10), the temperature is 40-90°C until the solution pH reaches 1.0-1.5.

The disadvantages of this method are the increased acidity of the resulting solution and the high toxicity of the concentrations of hydrochloric acid used.

A method is known for producing an iron- and aluminum-containing coagulant from thermal power plant ash or clay (RU Patent No. 2122975, published on 10.12.1998), which includes leaching metal oxides with a solution of sulfuric acid and a chloride-containing component, settling or filtering the reaction mass, where waste from the tannery industry is used as chloride-containing components - a solution of table salt after washing raw hides or a spent pickling solution with a concentration of table salt in the reaction solution of 8-50 g / l, and the reaction mass is heated by exposure to direct or alternating current with electrodes made of carbon iron alloys.

The disadvantages include the low efficiency of the resulting coagulant in relation to suspended solids, chromium compounds and petroleum products, and the sediment formed during the coagulation process has a low filtration rate.

A method for producing a coagulating reagent is known (RU Patent No. 2085509, published on July 27, 1997), including treating red mud from alumina production with a 3-5% solution of hydrochloric acid at a solid:liquid ratio of 1:(5-10), treating the resulting solid residue with a 50-55% solution of sulfuric acid at 100-110°C and a solid:liquid ratio of 1:(6-8), filtering the pulp and adding concentrated sulfuric acid to the resulting solution until its total content in the solution is 25-50 wt.%, after which the solution is kept for 10-20 hours and the precipitate is separated. The resulting coagulant contains, by weight: Al ₂ O ₃ 2 - 10; Fe ₂ O ₃ 2 -10; H ₂ SO _4total. 40 – ₆₀ , including _H2SO4free 20 - 40; _{H2Ocryst .} up to 100. The degree of purification of industrial wastewater from suspended particles when using the obtained coagulant does not exceed 91%.

The disadvantages of this method are the use of highly concentrated sulfuric acid and the limited scope of application of the resulting reagent due to its high content of free sulfuric acid and low content of coagulating agents Al ₂ O ₃ and Fe ₂ O ₃ .

A known method for producing an iron-containing coagulant for wastewater treatment (USSR Author's Certificate No. 80463, published on January 1, 1949) involves preliminary oxidation of pyrite cinders with strong nitric acid, taken in an amount of 8-10 kg per amount of pyrite cinders required to obtain 1 ton of coagulant, followed by holding the cinder for 5-6 hours before boiling in heated sulfuric acid until setting begins. With this production method, the coagulant has the following composition: total iron, calculated as Fe ₂ O ₃ - 20-22.5%; ferrous iron - 0.20%; free sulfuric acid - 0.24%; insoluble residue - 25-28%.

The disadvantages of this method are its long duration, high toxicity of the acidic concentrated reagents used and low efficiency of iron leaching due to the onset of the iron passivation process.

A known method for producing an aluminum- and iron-containing coagulant (RU Patent No. 2818198, published April 25, 2024) is adopted as a prototype. It involves treating iron ore enrichment waste with sulfuric acid at a concentration of 40-50% at a solid-to-liquid ratio of 1:1 g/ml. Further mixing is carried out at a temperature of 90-100°C. For at least 60 minutes. The efficiency of leached iron and aluminum under these conditions is 26.03% and 31.5%, respectively.

The disadvantages of the method are the low iron content in the resulting coagulant due to the shorter duration of the leaching reaction, as well as the need to maintain a high reaction temperature.

The technical result is an increase in the efficiency of wastewater treatment and the disposal of waste from sulfuric acid production.

The technical result is achieved by using sulfuric acid production waste - pyrite cinders - as a solid compound, which is placed in a reactor with a stirrer and treated with a sulfuric acid solution with a concentration of 30 to 40% or a hydrochloric acid solution with a concentration of 15 to 20%, while the ratio of sulfuric acid production waste to the acid reagent is 1: 3.6 g / ml, the resulting suspension is stirred at a temperature of 50 to 75 ° C, a rotation speed of at least 300 rpm, while the stirring time when using sulfuric acid is at least 240 minutes, when using hydrochloric acid at least 60 minutes.

The method for obtaining a coagulant is explained by the following figures:

Fig. 1 - graph of the dependence of color change on the dose of a coagulant with the active substance iron (III) sulfate.

Fig. 2 - graph of the dependence of color change on the dose of a coagulant with the active substance iron (III) chloride.

Fig. 3 – graph of the dependence of the efficiency of iron leaching with 30% sulfuric acid on the stirring speed under the following conditions: solid:liquid ratio 1:3.6 g/ml, contact time 240 minutes, temperature 75°C.

The method is carried out as follows. Waste from sulfuric acid production - pyrite cinders - are a dark-brown powdery material containing, in terms of the oxide form: Fe ₂ O ₃ - 72.5%, SiO ₂ - 14.6%, SO ₃ - 5.06%, Al ₂ O ₃ - 2.83%, MgO - 0.87%, Na ₂ O - 0.75%, ZnO - 0.67%, CuO - 0.62%, CaO - 0.56%, BaO - 0.54%, other impurities <1%. Pyrite cinders are placed in a reactor with a stirrer and treated with a sulfuric acid solution with a concentration of 30 to 40% or a hydrochloric acid solution with a concentration of no more than 20%. The sulfuric acid production waste to acid ratio is 1:3.6 g/ml. The suspension is then stirred at normal atmospheric pressure at a minimum rotation speed of 300 rpm, maintaining a temperature between 50°C and 75°C. The stirring time is at least 240 minutes when using sulfuric acid, and at least 60 minutes when using hydrochloric acid. The resulting suspension is filtered through a paper filter to separate the solid and liquid phases. The solid phase—a powdery precipitate—is discarded. The liquid phase, containing iron ions, is poured into a container, and a sample is collected for quantitative analysis of the iron content using an ICPE-9000 Shimadzu inductively coupled plasma atomic emission spectrometer.

Next, a model color solution based on sodium humate is prepared to test the performance of the resulting coagulants. A 50 g sample of sodium humate is transferred to a 2 ^dm³ flask, 1 ^dm³ of distilled water heated to 40 to 50°C is added, and the mixture is thoroughly mixed. The flask is then sealed and the solution is left to stand for at least 24 hours. The solution is then filtered through a paper filter and diluted with distilled water until the model solution reaches a color of 50°, as determined by the color scale.

The prepared color model solution is poured into transparent containers, and an equal dose of coagulant is added to each container. The pH of the model solutions is adjusted to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 using 0.1N NaOH and HCl solutions. The solutions are then mixed on a laboratory shaker and allowed to settle for at least 30 minutes. The resulting suspensions are then filtered, the resulting solid phase is discarded, and the liquid phase is sent for analysis of the remaining color using a DR5000 spectrophotometer. Photometric color determination is performed in a 5 cm long cuvette.

The lowest effective coagulant application rate is determined. 1.0 ^dm³ of ^the color model solution is poured into 1 dm³ glass laboratory beakers, placed on a magnetic stirrer, and the stirring speed is set to 140 rpm, with the heating temperature set to 20 to 21 ^° C. Working doses of the coagulant are then added to the model solutions, and stirring is continued for 3 minutes. The stirring speed of the resulting suspensions is then gradually reduced to 40 rpm over 10 seconds, and stirring is continued for at least 15 minutes. The solutions are then allowed to settle for at least 30 minutes. The solutions are then filtered through membrane filters to separate the solid and liquid phases. The solid phase is discarded, and the liquid phase is analyzed for residual color using a DR5000 photometer. The coagulant dose that reduces the solution color from 50° to 20° is considered the minimum effective coagulant dose. If the iron leaching efficiency from pyrite calcine is less than 26%, coagulant production is impractical, as the dose applied for water treatment would be too high, leading to secondary contamination of the treated water.

The method is illustrated by the following examples.

Example 1. 5 g of pyrite cinders are treated with 18 ml of 20% sulfuric acid at 20°C for 120 minutes. The iron leaching efficiency is 1.4% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 2. 5 g of pyrite cinders are treated with 18 ml of 30% sulfuric acid at 20°C for 120 minutes. The iron leaching efficiency is 1.8% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 3. 5 g of pyrite cinders are treated with 18 ml of 40% sulfuric acid at 20°C for 120 minutes. The iron leaching efficiency is 3.1% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 4. 5 g of pyrite cinders were treated with 18 ml of 50% sulfuric acid at 20°C for 120 minutes. The iron leaching efficiency was 3.1%, and iron passivation was also observed (Table 3). The resulting iron leaching efficiency does not meet the accepted requirement. Further study of the coagulant is not advisable.

Example 5. 5 g of pyrite cinders are treated with 18 ml of 20% sulfuric acid at 75°C for 240 minutes. The iron leaching efficiency is 14.0% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 6. 5 g of pyrite cinders are treated with 18 ml of 30% sulfuric acid at 50°C for 120 minutes. The iron leaching efficiency is 13.0% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 7. 5 g of pyrite cinders are treated with 18 ml of 30% sulfuric acid at 75°C for 120 minutes. The iron leaching efficiency is 22.0% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 8. 5 g of pyrite cinders are treated with 18 ml of 30% sulfuric acid at 75°C for 240 minutes. The iron leaching efficiency is 27.0% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition.

Example 9. 5 g of pyrite cinders are treated with 18 ml of 40% sulfuric acid at 50°C for 120 minutes. The iron leaching efficiency is 23.0% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 10. 5 g of pyrite cinders are treated with 18 ml of 40% sulfuric acid at 75°C for 120 minutes. The iron leaching efficiency is 25.0% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 11. 5 g of pyrite cinders are treated with 18 ml of 40% sulfuric acid at 50°C for 240 minutes. The iron leaching efficiency is 26.0% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition.

Example 12. Pyrite cinders in the amount of 5 g are treated with 15 ml of sulfuric acid of 40% concentration at a temperature of 50° C. It is observed that it is impossible to evenly mix the contacting media, which makes this experiment unrealistic.

Example 13. 5 g of pyrite cinders are treated with 20 ml of 40% sulfuric acid at 50°C for 240 minutes. The iron leaching efficiency is 26.3% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition. The iron leaching efficiency at the selected volume of acid reagent changes insignificantly compared to the iron leaching efficiency at a waste to acid reagent ratio of 1:3.6 g/ml, indicating excess acid reagent consumption.

Example 14. 5 g of pyrite cinders are treated with 22.5 ml of 40% sulfuric acid at 50°C for 240 minutes. The iron leaching efficiency is 26.1% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition. The iron leaching efficiency at the selected volume of acid reagent changes insignificantly compared to the iron leaching efficiency at a waste to acid reagent ratio of 1:3.6 g/ml, indicating excess consumption of the acid reagent. Thus, the selected waste to acid reagent ratio of 1:3.6 g/ml is the minimum possible and effective.

Example 15. 5 g of pyrite cinders are treated with 18 ml of 40% sulfuric acid at 75°C for 240 minutes. The iron leaching efficiency is 34.0% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition. The resulting suspension is filtered with a blue ribbon filter with a pore size of 2 μm. The solid phase is sent for disposal. The liquid phase, which is the coagulant, is pumped to another tank, where the iron leaching efficiency is assessed to calculate the coagulant dosage. Next, the optimal pH is selected for the most effective purification of the model color solution with the coagulant (Table 1). Then, the lowest effective coagulant application rate for iron oxide is determined. According to the test results, the coagulant showed the highest efficiency at pH=6-7, the minimum effective dose of iron oxide added to the model color solution is 667 mg/l.

Table 1 – The effect of pH on the coagulation process for a coagulant with iron (III) sulfate as the active substance

Item No. Initial color of the solution Abs, before cleaning pH Abs, after coagulation Color of the solution after cleaning 1 50 0.071 1 0, 024 17 2 50 0.071 2 0, 024 17 3 50 0.071 3 0.025 17 4 50 0.071 4 0.013 9 5 50 0.071 5 0.010 7 6 50 0.071 6 0.009 6 7 50 0.071 7 0.008 6 8 50 0.071 8 0.061 43 9 50 0.071 9 0, 066 46 10 50 0.071 10 0.075 53 11 50 0.071 11 0.089 63 12 50 0.071 12 0.093 65

During the experiment, it was revealed that the coagulant was most effective at pH = 6-7, while it demonstrated its performance in a wide pH range from 1 to 9.

Example 16. 5 g of pyrite cinders are treated with 18 ml of 10% hydrochloric acid at 20°C for 120 minutes. The iron leaching efficiency is 1.4% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 17. 5 g of pyrite cinders are treated with 18 ml of 20% hydrochloric acid at 20°C for 120 minutes. The iron leaching efficiency is 24% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 18. 5 g of pyrite cinders are treated with 18 ml of 30% hydrochloric acid at 20°C for 120 minutes. Iron leaching efficiency is 50% (Table 3). Further study of the coagulant's effectiveness is impractical due to the high toxicity of hydrochloric acid at this concentration.

Example 19. 5 g of pyrite cinders are treated with 18 ml of 15% hydrochloric acid at 20°C for 120 minutes. The iron leaching efficiency is 11.0% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 20. 5 g of pyrite cinders are treated with 18 ml of 15% hydrochloric acid at 50°C for 60 minutes. The iron leaching efficiency is 24.0% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Example 21. 5 g of pyrite cinders are treated with 18 ml of 15% hydrochloric acid at 50°C for 120 minutes. The iron leaching efficiency is 27.0% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition.

Example 22. 5 g of pyrite cinders are treated with 18 ml of 15% hydrochloric acid at 75°C for 60 minutes. The iron leaching efficiency is 31.0% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition.

Example 23. 5 g of pyrite cinders are treated with 18 ml of 15% hydrochloric acid at 75°C for 120 minutes. The iron leaching efficiency is 34.0% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition.

Example 24. 5 g of pyrite cinders are treated with 18 ml of 20% hydrochloric acid at 50°C for 60 minutes. The iron leaching efficiency is 30% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition.

Example 25. 5 g of pyrite cinders are treated with 18 ml of 20% hydrochloric acid at 50°C for 120 minutes. The iron leaching efficiency is 32% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition.

Example 26. 5 g of pyrite cinders are treated with 18 ml of 20% hydrochloric acid at 75°C for 120 minutes. The iron leaching efficiency is 42% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition.

Example 27. 5 g of pyrite cinders are treated with 18 ml of 20% hydrochloric acid at 75°C for 60 minutes. The iron leaching efficiency is 38% (Table 3). The resulting iron leaching efficiency satisfies the accepted condition. The resulting suspension is filtered using a "blue ribbon" membrane filter with a pore size of 2 μm. The solid phase is sent for disposal. The liquid phase, which is the coagulant, is poured into another container, where the iron leaching efficiency is assessed to calculate the coagulant dosage. Next, the optimal pH is selected for the most effective purification of the model color solution with the coagulant (Table 2). Then, the lowest effective coagulant application rate for iron oxide is determined. According to the test results, the coagulant showed the highest efficiency at pH=1-3, the minimum effective dose of iron oxide added to the model color solution is 82.5 mg/l.

Table 2 – The effect of pH on the coagulation process for a coagulant with iron (III) chloride as the active substance

Item No. Initial color of the solution Abs, before cleaning pH Abs, after coagulation Color of the solution after cleaning 1 50 0.070 1 0.012 9 2 50 0.070 2 0.012 9 3 50 0.070 3 0.008 6 4 50 0.070 4 0.013 10 5 50 0.070 5 0.027 19 6 50 0.070 6 0.026 19 7 50 0.070 7 0.024 17 8 50 0.070 8 0.031 22 9 50 0.070 9 0.079 56 10 50 0.070 10 0.079 56 11 50 0.070 11 0.081 58 12 50 0.070 12 0.085 60

Example 28. 5 g of pyrite cinders are treated with 18 ml of 10% hydrochloric acid at 75°C for 120 minutes. The iron leaching efficiency is 21.0% (Table 3). The resulting iron leaching efficiency does not meet the accepted condition. Further study of the coagulant is not advisable.

Based on the results of the experiments shown in Fig. 1 and Fig. 2, it can be concluded that the effective doses of coagulants for the model color solution are, for iron oxide: for a coagulant with the active substance iron (III) sulfate - 667 mg/l, iron (III) chloride - 82.5 mg/l.

Table 3 – results of the experiments

Item No. Sulfuric acid concentration, % Solid:liquid ratio, g/ml Temperature, °C Time, min Iron leaching efficiency Fe, % For sulfuric acid 1 20 1:3.6 20 120 1.4 2 30 1:3.6 20 120 1.8 3 40 1:3.6 20 120 3.1 4 50 1:3.6 20 120 3.1 5 20 1:3.6 75 240 14.0 6 30 1:3.6 50 120 13.0 7 30 1:3.6 75 120 22.0 8 30 1:3.6 75 240 27.0 9 40 1:3.6 50 120 23.0 10 40 1:3.6 75 120 25.0 11 40 1:3.6 50 240 26.0 12 40 1:3 50 - - 13 40 1:4 50 240 26.3 14 40 1:4.5 50 240 26.2 15 40 1:3.6 75 240 34.0 For hydrochloric acid 16 10 1:3.6 20 120 1.4 17 20 1:3.6 20 120 24.0 18 30 1:3.6 20 120 50.0 19 15 1:3.6 20 120 11.0 20 15 1:3.6 50 60 26.0 21 15 1:3.6 50 120 27.0 22 15 1:3.6 75 60 31.0 23 15 1:3.6 75 120 34.0 24 20 1:3.6 50 60 30.0 25 20 1:3.6 50 120 32.0 26 20 1:3.6 75 120 42.0 27 20 1:3.6 75 60 38.0 28 10 1:3.6 75 120 21.0

The highest efficiency of iron leaching from sulfuric acid production waste was achieved with a sulfuric acid concentration of 30 to 40% and hydrochloric acid concentration of 15 to 20%; at a reaction temperature of 50° to 75° C and a reaction time of at least 240 min for the coagulant obtained with sulfuric acid and at least 60 min for the coagulant obtained with hydrochloric acid, at a stirring speed of at least 300 rpm, and was: 34% for the coagulant obtained with sulfuric acid and 42.0% for hydrochloric acid.

Increasing the efficiency of wastewater treatment and recycling of sulfuric acid production waste is achieved by producing a coagulant for water purification by treating sulfuric acid production waste – pyrite cinders – with solutions of sulfuric acid from 30% to 40% or hydrochloric acid from 15 to 20%.

Claims (1)

A method for producing an iron-containing coagulant from pyrite cinders, including treating a solid compound containing iron oxides with an acid solution, followed by testing the performance of the resulting coagulant using a model solution and determining the minimum effective dose of the coagulant required to reduce the color of water from 50 to 20 degrees of color, characterized in that the solid compound is waste from sulfuric acid production - pyrite cinders, which are placed in a reactor with a stirrer and treated with a solution of sulfuric acid with a concentration of 30 to 40% or a solution of hydrochloric acid with a concentration of 15 to 20%, wherein the ratio of waste from sulfuric acid production to the acid reagent is 1: 3.6 g / ml, the resulting suspension is stirred at a temperature of 50 to 75 ° C, a rotation speed of at least 300 rpm, while the stirring time when using sulfuric acid is at least 240 min, when using hydrochloric acid for at least 60 minutes.