RU2845781C1 - Method for defluorination of waste water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to defluorination of industrial waste water by precipitation and can be used to treat high-fluorine waste water, production of wet-process phosphoric acid, mineral fertilizer or aluminium metal. Method for defluorination of waste water involves treatment thereof with a calcium-containing reagent until achieving pH 9-11.5 and subsequent separation of the liquid and solid phases by settling. Calcium-containing reagent used is a waste – steel-smelting slag, pre-calcined at temperature 800 °C. Waste water is treated with steel-smelting slag with ratio calcium/fluorine equal to (1.0-2.25):1.

EFFECT: highly efficient method of purifying waste water from fluorides with their initial content of more than 100 g/dm³.

1 cl, 6 ex

Description

The invention relates to the field of defluorination of industrial wastewater, in particular, to a method for purifying wastewater from fluorides by precipitation and can be used to purify highly fluorinated wastewater from the production of extraction phosphoric acid, mineral fertilizers or metallic aluminum.

A method for wastewater defluoridation is known, which includes treating wastewater with a calcium-containing reagent, in particular, calcium hydroxide, followed by the introduction of hydrated aluminum sulfate, resulting in the formation of an insoluble calcium-aluminum complex (G.Ei Diwani, Sh.K. Amin, N.K. Attia. Fluoride pollutants removal from industrial wastewater // Bulletin of the National Research Centre. - 2022. - 46(143). - P.1-9. DOI:10.1186/s42269-022-00833-w).

The disadvantage of this method is the high reagent costs of hydrated aluminum sulfate for the formation of calcium-aluminum complexes and the lack of the ability to purify wastewater with a fluoride content of more than 528 mg/l.

A method of wastewater defluoridation is known using aluminum oxide and activated aluminum oxide with hydrochloric acid at an initial fluoride ion content of no more than 10 mg/dm3. The defluoridation process is carried out in hydrocyclones, and aluminum-containing reagents are fed in the form of pulp. It was shown that the efficiency of fluoride ion removal was 49.5 and 80% for aluminum oxide and activated aluminum oxide, respectively (Gayatree Patra, Priyam Das, S. Chakraborty, B. C. Meikap. Removal of fluoride from wastewater using HCl-treated activated alumina in a ribbed hydrocyclone separator // Journal of Environmental Science and Health, Part A.-2018.-53(7).- P.601-608. DOI:10.1080/10934529.2018.1429728).

The disadvantages of this method are the use of expensive aluminum oxide in the form of pulp, which in turn does not ensure the completeness of the aluminum fluoride formation process. As a result, the resulting sludge will contain a significant amount of unreacted aluminum oxide, leading to an overconsumption of the reagent.

A method of wastewater defluoridation is known using the contact-sorption method by treating it with coagulants in the form of aluminum or iron salts (sulfate, chloride or oxychloride, in particular for aluminum) at a dose of at least 150 mg / l (in terms of Al2O3). Then the coagulant dose is reduced to 20-30 mg / l, thereby increasing the efficiency of water defluoridation (Krasavtseva E.A. Wastewater treatment of Lovozersky GOK LLC from fluorine ions by chemical coagulation // Proceedings of the Fersman Scientific Session of the GI KSC RAS. - 2020. - No. 17. - P. 297-301).

The disadvantages of this method are the high consumption of expensive coagulants based on aluminum or iron, the overconsumption of which negatively affects the subsequent process of additional treatment, as well as the need to create a velocity gradient for the effective mixing of wastewater and reagents.

The closest to the claimed method (prototype) is the method of defluoridation of wastewater with lime milk until pH 9-11 is reached in the presence of sulfate, calcium chloride or phosphogypsum (Patent of the Russian Federation 2570467 C02F 1/58 Sharipov T.V., Knzyabulanova G.S., Delmukhametova A.I., Shayakhmetov D.I., Mustafin A.G., Shangaraev K.R., patent publication 10/27/2015).

A significant disadvantage of this method is the need to use expensive calcium sulfate or chloride in the prototype, thereby increasing reagent costs and the cost of the purification process, as well as secondary contamination of water with chloride, sulfate anions and aluminum compounds.

The objective of this invention is to develop a modern, highly effective method for purifying wastewater from fluorides with an initial content of more than 100 g/ ^dm3 .

The task at hand is solved by defluoridating wastewater by treating it with calcium-containing waste until a pH of 9-11.5 is reached, followed by separating the liquid and solid phases by settling, where the process of sedimentation of the insoluble part occurs, while the waste used as a calcium-containing reagent is steel slag (dust), previously subjected to heat treatment at a temperature of 800°C and a calcium:fluorine ratio of (1.0-2.25):1.

The essence of the proposed method and the results achieved can be more clearly illustrated by the following examples.

EXAMPLE 1

Fluorine-containing wastewater from a gas cleaning unit of the aluminum metal production process with a fluoride ion content of: F ^- - 115 g/l; pH < 1 is treated with steelmaking slag preliminarily heat-treated at a temperature of 800°C and a ratio of Ca:F = 1:1, the process is carried out for 10 minutes until a pH of 9.0 is achieved. The residual content of fluoride ions is 0.055 g/ ^dm3 (purification efficiency 99.95%).

EXAMPLE 2

Fluorine-containing wastewater from a gas cleaning plant in the process of producing metallic aluminum with a fluoride ion content of: F ^- - 115 g/l; pH < 1 is treated with steelmaking waste pre-calcined at a temperature of 800°C and a ratio of Ca:F = 1.25:1, the process is carried out for 10 minutes until a pH of 9.5 is achieved. The residual content of fluoride ions is 0.050 g/ ^dm3 (purification efficiency 99.95%).

EXAMPLE 3

Fluorine-containing wastewater from a gas cleaning plant for the production of metallic aluminum containing fluoride ions: F ^- - 115 g/l; pH < 1 is treated with steelmaking waste pre-calcined at a temperature of 800°C and a ratio of Ca:F = 1.5:1, the process is carried out for 10 minutes until a pH of 10.0 is achieved. The residual content of fluoride ions is 0.045 g/ ^dm3 (purification efficiency 99.95%).

EXAMPLE 4

Fluorine-containing wastewater from a gas cleaning plant for the production of metallic aluminum with a fluoride ion content of: F ^- - 115 g/l; pH < 1 is treated with steelmaking waste pre-calcined at a temperature of 800°C and a ratio of Ca:F = 1.75:1, the process is carried out for 10 minutes until a pH of 10.5 is achieved. The residual content of fluoride ions is 0.040 g/ ^dm3 (purification efficiency 99.95%).

EXAMPLE 5

Fluorine-containing wastewater from a gas cleaning plant in the process of producing metallic aluminum with a fluoride ion content of: F ^- - 115 g/l; pH < 1 is treated with steelmaking waste pre-calcined at a temperature of 800°C and a ratio of Ca:F = 1.0:1, the process is carried out for 10 minutes until a pH of 11.0 is achieved. The residual content of fluoride ions is 0.035 g/ ^dm3 (purification efficiency 99.95%).

EXAMPLE 6

Fluorine-containing wastewater from a gas cleaning plant in the process of producing metallic aluminum with a fluoride ion content of: F ^- - 115 g/l; pH < 1 is treated with steelmaking waste pre-calcined at a temperature of 800°C and a ratio of Ca:F = 2.25:1, the process is carried out for 10 minutes until a pH of 11.5 is achieved. The residual content of fluoride ions is 0.030 g/ ^dm3 (purification efficiency 99.95%).

The presented examples show that the use of steel-smelting waste as a calcium-containing reagent allows for a significant reduction in reagent costs for the cleaning process. The use of steel-smelting waste allows for a reduction in secondary water pollution with fluoride and sulfate anions. In addition, the advantage of the proposed method is the high efficiency of cleaning high-fluoride wastewater (> 99.99%), due to which the residual content of fluoride ions ranges from 0.055 g/dm ³ to 0.030 g/dm ³ .

Claims (1)

A method for defluoridating wastewater, which consists in treating fluorine-containing wastewater with calcium-containing waste until a pH of 9-11.5 is reached, followed by separation of the liquid and solid phases by settling, characterized in that the calcium-containing reagent used is steel slag calcined at a temperature of 800°C, and the wastewater is treated at a calcium/fluorine ratio of (1.0-2.25):1.