RU2283814C1 - Process of treating waste water polluted with stone-cutting production waste - Google Patents

Abstract

FIELD: waste water treatment.

SUBSTANCE: invention relates to technology of treating waste waters polluted with suspended stone particles and ensures obtaining product that can be used as coagulant. In a waste water treatment process including coagulation and precipitation of suspended materials, part of settled stone slurry is separated , mixed with phosphoric acid and/or its soluble salts on the basis of 5-10 kg per 100 L stone slurry, kept until gas evolution ends, and thus obtained product is placed in water being treated in amount 1-3 ml per 1 L water.

EFFECT: accelerated precipitation of suspended stone particles and simplified process.

2 tbl, 32 ex

Description

The invention relates to a technology for wastewater treatment contaminated with suspended stone particles.

A known method of purification of water contaminated with inorganic substances by introducing a sorbent, flocculant, coagulant and mineral opacifier; as a sorbent and a mineral opacifier, a mixture of hydrolyzed coarse and finely dispersed aluminosilicates is introduced in a ratio between them of 1: 1-2: 1 in an amount of 20-900 mg / l; colloidal dispersed aluminosilicates in an amount of 1-100 mg / l are introduced as a flocculant , and as a coagulant make the composition of molecularly dispersed hydroxides of aluminum, silicon, iron, titanium, calcium, magnesium in a total amount of 1-80 mg / l, RU 2143403.

This method is quite complicated, because along with the introduction of the coagulant, it also requires the introduction of a flocculant, sorbent and mineral opacifier. The composition of molecularly dispersed hydroxides of aluminum, silicon, iron, titanium, calcium, magnesium used as a coagulant is very expensive and difficult to implement.

A known method of treating wastewater contaminated with waste stone-cutting production, including coagulation and sedimentation of suspended solids.

According to this method, adopted as a prototype of the present invention, a coagulant in the form of Al ₂ (SO ₄ ) ₃ and a flocculant (polyacrylamide) are introduced into contaminated water, see SNiP 20402-84 (a copy of the link is attached).

The main disadvantage of this method is the low deposition rate of suspended solids, which are fine stone particles.

Processed stones have a complex chemical and mineralogical composition and are insoluble compounds of aluminum, calcium, titanium, iron, silica and other elements (Chemical Encyclopedia, Moscow, 1961, T.1, c.c.847-852, 888-894).

Each particle - a fragment of the destroyed stone - has on its surface hydrated, carbonate surface compounds Al (OH) ₃ , Fe (OH) ₃ , SiO ₂ · nH ₂ O and hydroxyl and carboxyl groups:

The coagulating agent in the prototype method is Al (OH) ₃ , which is formed by hydrolysis of Al ₂ (SO ₄ ) ₃ . However, the rate of this hydrolysis is extremely low and, accordingly, the deposition rate of suspended stone particles is low. To accelerate this process, the prototype method additionally uses a flocculant-polyacrylamide. In addition, the prototype method requires the continuous introduction of new batches of reagents - Al ₂ (SO ₄ ) ₃ and polyacrylamide.

This significantly increases the cost and complicates the process, but, nevertheless, does not provide the deposition rate of suspended stone particles, sufficient to create a closed water cycle.

The present invention is based on the solution of the problem of increasing the rate of deposition of suspended stone particles in the process of wastewater treatment, contaminated with waste stone-cutting production, simplification and cheapening of this process.

According to the invention, this problem is solved due to the fact that in the method of treating wastewater contaminated with waste from stone-cutting production, including coagulation and sedimentation of suspended solids, part of the settled stone slurry is recovered, mixed with phosphoric acid at the rate of 5-10 kg per 100 l of stone slime maintain the mixture until gas evolution ceases and the resulting product is introduced into the purified water in an amount of 1-3 ml per 1 liter of purified water.

The applicant has not identified sources containing information about technical solutions identical to the present invention, which allows us to conclude that it meets the criterion of "novelty."

The treatment of stone sludge with phosphate ingredients leads to the decomposition of carbonate and hydroxide surface compounds and the replacement of functional groups with phosphate.

The processes occurring in this case can be represented by the following schemes:

1.3CaCO ₃ + 2H ₃ PO ₄ → Ca ₃ (PO ₄ ) ₂ ↓ + CO ₂ ↑ + H ₂ O

2. Al (OH) ₃ + H ₃ PO ₄ → ↓ AlPO ₄ + 3H ₂ O

3. Fe (OH) ₃ + H ₃ PO ₄ → ↓ FePO ₄ + 3H ₂ O

4.3Mg (OH) ₂ + 2H ₃ PO ₄ → Mg ₃ (PO ₄ ) ₂ + 3H ₂ O

Surface = SiOH, = FeOH, -CaOH and other hydroxyl groups are replaced by phosphate (= PO ₄ ) functional groups.

As a result of chemisorption transformations, new modified particles have a changed surface chemical composition, since surface compounds are formed: phosphates of calcium, iron, aluminum and other elements.

Adopted conditions for the implementation of the method (room temperature, atmospheric pressure, pH = 2.5-5) can save the mineralogical structure of stone nanoparticles.

The resulting particles differ from suspended particles of stone sludge by the presence of phosphate functional groups on their surface and are similar in structure. In this case, in accordance with the Le Chatelier principle, the system seeks intensive coagulation of suspended particles, rapid deposition and compaction of sediment.

The applicant has not found any sources of information containing information about the impact of the claimed distinctive features on the technical result achieved as a result of their implementation. This, according to the applicant, indicates that this technical solution meets the criterion of "inventive step".

The claimed method allows you to quickly clean water contaminated with waste stone-cutting production; however, instead of the expensive coagulants and flocculants, these wastes themselves and very cheap phosphoric acid are used. The product obtained as a result of water treatment can be successfully disposed of:

- as a coagulant for further wastewater treatment from a number of pollutants;

- as a sorbent for cleaning the soil from compounds of heavy metals;

- as an ingredient in fire retardant coatings.

The implementation of the method is as follows.

Example 1. Obtaining a product from stone sludge (coagulant).

Two parallel horizontal settling tanks with a total capacity of 250 m ³ were filled with waste water contaminated with stone-cutting production waste containing 2000 mg / l of suspended solids in terms of dry matter with particle sizes of 1-60 nm.

Primary precipitation was carried out within 24 hours. In a 200 L barrel, 100 L of stone slurry was placed, 5 kg of concentrated phosphoric acid was added with periodic stirring, and the mixture was kept until gas evolution ceased (48 hours). As a result, the precipitated stone slurry has the following chemical composition (in wt.%): SiO ₂ - 26%, Al ₂ O ₃ - 28%, Fe ₂ O ₃ - 8%, MgO - 22%, CaO - 0.2%, the rest is structural water and intermicellar fluid having a pH = 5, a density of 1.4 g / cm ³ .

After interaction with phosphoric acid, phosphoric acid surface compounds (FePO ₄ , AlPO ₄ , Ca (PO ₄ ) ₂ , etc.) formed on the surface of primary nanometric particles of stone sludge, and surface = Si-OH, = FeOH, -CaOH and other hydroxyl groups nanometric primary particles are replaced by phosphate (= PO ₄ ) functional groups.

Example 2

The same as in example 1, but to 100 l of settled stone sludge was added 7 kg of concentrated phosphoric acid. After periodic stirring for 24 hours, a product with a density of 1.4 g / cm ³ and pH = 3 was obtained.

Example 3

The same as in example 1, but to 100 l of stone sludge was added 10 kg of concentrated phosphoric acid. After 24 hours, a product was obtained with a density of 1.35 g / cm ³ , pH = 2.5.

Example 4

Same as in example 1, but 3 kg of concentrated phosphoric acid was added to 100 l of stone sludge. Got a product with a density of 1.3 g / cm ³ and pH = 8.

Example 5

The same as in example 1, but to 100 l of stone sludge was added 15 kg of concentrated phosphoric acid. The density of the obtained product is 1.4 g / cm ³ , pH = 1.5.

The resulting products (examples 1-5) differ significantly in pH; they were then used as coagulants to clarify the waste water of stone-cutting production. The results of water clarification experiments are given below.

Examples 6-30. Clarification of wastewater.

25 experiments were carried out on clarification of stone-cutting production wastewater with an initial concentration of suspended solids in all experiments of 2000 mg / l by products obtained from stone sludge (coagulants) in accordance with examples 1-5. The coagulants at the same time had a gradation of pH from 1.5 to 8. Coagulant with each pH value was introduced into the purified water in a volume of from 0.5 to 6.0 ml per 1 liter of purified water (examples 6-30). The experiments were carried out in a vertical sedimentation tank with a capacity of 15 m ³ , in which 10 m ^{3 of} purified water was placed. The concentration of suspended solids before and after clarification of the water was determined by the gravimetric method in accordance with the PND methodology 14.1.2.110-97. The sedimentation rate of suspended particles was determined by linear measurements of the displacement of the front of the deposited particles. When determining the concentration and deposition rate of suspended solids in water in each example, 3 measurements were carried out to increase the accuracy of the results and average values of the results of these measurements are listed in table 1.

Table 1 coagulant pH Example No. Coagulant volume (ml) per 1 liter of purified water The average concentration of suspended solids in water after clarification (mg / g) The sedimentation rate of suspended solids in water (cm / min) 5 (as in example 1) 6 0.5 180 0.1 7 1,0 eleven 2 8 2.0 6 6 9 3.0 5 10 10 6.0 5 10 3 (as in example 2) eleven 0.5 160 0.2 12 1,0 10 3 13 2.0 5 7 fourteen 3.0 four eleven fifteen 6.0 four eleven 2.5 (as in example 3) 16 0.5 150 0.25 17 1,0 9 3,5 eighteen 2.0 4,5 7.5 19 3.0 four 12 twenty 6.0 four 12 8 (as in example 3) 21 0.5 250 0.05 22 1,0 140 0.08 23 2.0 110 0.1 24 3.0 90 0.1 25 6.0 70 0.15 1.5 (as in example 5) 26 0.5 150 0.25 27 1,0 9 3,5 28 2.0 four 12 29th 3.0 four 12 thirty 6.0 four 12

The analysis of the results shown in table 1 shows that the optimal boundaries of the mass values of concentrated phosphoric acid introduced per 100 l of stone sludge are in the range from 5 to 10 kg, which corresponds to the pH range of the resulting coagulant 5-2.5. At pH above 5 (examples 21-25, pH = 8), the concentration of suspended solids in the water after clarification is unacceptably high, and their deposition rate is very low. At a pH of less than 2.5 (example 26-30, pH = 1.5), the flow rate of H ₃ PO _{4 is} unreasonably high (15 kg per 100 l), and the quantitative parameters of the deposition of suspended particles are almost the same as with the flow rate of H ₃ PO ₄ 10 kg per 100 l (pH = 2.5).

From table 1 it is also seen that the optimal boundaries of the volume introduced into the purified water of the product leave from 1 to 3 ml per 1 liter of water.

Example 31

The treatment of soil contaminated with lead compounds was carried out as a secondary product obtained by the deposition of suspended particles in accordance with the claimed method.

Adding the product to the soil and testing (quantitative determination of total lead and its mobile forms) was carried out according to test methods RD 52.18.191.89 and PND f. 16.4-97.

The results of the experiments.

Before soil cultivation, the total lead content was 108.9 mg / kg. The content of mobile forms is 25.2 mg / kg. After soil treatment with the product, the content of mobile forms of lead is 0.6 mg / g, i.e. 40 times reduction achieved.

Example 32

For the treatment of wastewater contaminated with inorganic substances, the same product was introduced into a sample containing water-soluble compounds of copper, nickel, cadmium, lead, and iron as in Example 31 at the rate of 20-200 mg per 1 liter of purified water.

The sample was shaken for 2-3 minutes, settled for 1 hour, and the content of these substances was determined before and after contact.

Concentrations of pollutants before and after water treatment are shown in table 2.

table 2 Initial pollutant concentration The concentration of pollutants after cleaning Degree of purification Pollutant element With _ref mg / l C _ost mg / l % Cu ²⁺ 1.95 0.002 99.8 Ni ²⁺ 0.96 0.01 98.8 Cd ²⁺ 0.01 0.001 90.0 Pb ²⁺ 0.14 <0.001 96.0 Fe ³⁺ 0.73 0.01 98.3

The method can be implemented using simple equipment available at each stone processing enterprise, which determines the compliance of the invention with the criterion of "industrial applicability".

Claims (1)

A method of treating wastewater contaminated with waste from stone-cutting production, including coagulation and sedimentation of suspended solids, characterized in that a part of the settled stone sludge is recovered, mixed with phosphoric acid at the rate of 5-10 kg per 100 l of stone sludge, the mixture is kept until gas evolution ceases and inject the resulting product into the purified water in an amount of 1-3 ml per 1 liter of purified water.