RU2835103C1 - Method of purifying waste water from sulphides - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to purification of natural and waste water from industrial enterprises from sulphides. Method of purifying waste water from sulphides involves reacting a complex of iron with ethylenediaminetetraacetate and a stabilizer with water containing sulphide ions. Stabilizer used is nitrilotrimethylene phosphonic acid in amount of 0.01–0.1% of the weight of the absorption solution.

EFFECT: reduced specific consumption of complexing agent - ethylenediamineteraacetate per gram of formed sulfur and reduced corrosion of equipment.

1 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of purification of natural and waste water from industrial enterprises (tanneries, pulp and paper, chemical, oil, etc.) from sulfides.

There are known methods for cleaning from sulfides and hydrogen sulfide using iron-containing reagents (iron hydrochloride, iron sulfate, etc.) by filtering water through a layer of granular filling pre-filled with an iron-containing reagent (see Klyachko V.A. Purification of Natural Waters / V.A. Klyachko, I.E. Apeltsin. Moscow: Stroyizdat, 1971, pp. 479-481; USSR patent No. 941303, 1982; Russian Federation patent No. 2285682, 2006; Russian Federation patent No. 2361822, 2009).

The general disadvantage of these methods is the high consumption of reagents used in the cleaning and regeneration process, capital and other costs during the construction and operation of filter equipment.

The closest to the proposed technical solution is a purification method that includes the oxidation-reduction interaction of hydrogen sulfide and sulfide ions with an iron complex of ethylenediaminetetraacetate (disodium salt - Trilon B), containing a stabilizer of di- and triethanolamines in an amount of 15-45 g/l (RU Patent No. 2042403, 1995).

The disadvantage of the known method is the increased corrosive aggressiveness of the iron complex of ethylenediaminetetraacetate towards structural steel, significant losses of the complexing agent per gram of sulfur obtained, high consumption (15-45 g/l) and costs for using the stabilizer - di- and triethanolamine.

The essence of the oxidation-reduction method of purification from hydrogen sulfide and sulfide ions is that trivalent iron ions, due to their relatively high oxidation-reduction potential, = +0.77v are an oxidizer for hydrogen sulfide and sulfide ions = -0.476v. The potential difference ensures a high rate and depth of conversion of sulfide ions into atomic sulfur. This is evidenced by the calculated value of the oxidation-reduction rate constant:

- Oxidizer

- Restorer

Where - standard potential = +0.77v,

- standard potential = -0.476v,

n is the number of electrons,

0.059 = ( ) at a temperature of 25°C.

The role of the complexing agent is to form a stable complex with Fe ³⁺ that does not hydrolyze and precipitates from the solution in the form of hydroxide, reducing the efficiency of oxidation. However, the high complexing ability of Trilon B with both divalent and trivalent iron ions (pK 14.27 and 25.0, respectively) has a negative effect on the amount of corrosion in the presence of the iron complex of Trilon B and, as a consequence, affects the increase in its consumption on the amount of sulfur formed.

The technical objective of this invention is to reduce the specific consumption of the complexing agent - ethylenediaminetetraacetate (Trilon B) per gram of sulfur formed, and to reduce the amount of corrosion of equipment due to high corrosive aggressiveness towards structural steel.

The technical task is achieved by the fact that a method for purifying wastewater from sulfides is declared, which includes the interaction of an iron complex with ethylenediaminetetraacetate (Trilon B) and a stabilizer with water containing sulfide ions, characterized in that nitrilotrimethylenephosphonic acid is used as a stabilizer in an amount of 0.01-0.1% of the mass of the absorption solution.

The stabilizer used in the claimed method is a complexing agent - nitrilotrimethylenephosphonic acid (NTP), taken in an amount of 0.01-0.1% of the mass of the absorption solution, which forms a virtually insoluble complex with iron ions (solubility 5.5⋅10 ^-4 g / l) (see N.M. Dyatlova, V.Ya. Temkina, K.I. Popov, Complexones and Complexonates of Metals. Moscow: Chemistry, 1988. 544 p.). The resulting precipitate forms a protective film on the surface of the metal, which protects it from further corrosion and reduces the consumption of Trilon B in the process of precipitation of sulfur from the solution.

A comparison of the claimed technical solution with the prototype shows that it meets the “novelty” criterion.

The claimed technical solution can be implemented using known technological and technical means, therefore it meets the criterion of “industrial applicability”.

During the patent research, the claimed set of features was not identified, therefore it can be assumed that the technical solution meets the criterion of “inventive step”.

The claimed method is illustrated by the following examples:

A solution of sodium sulfide with a concentration of 3.9 g/l (0.1N solution) is gradually added to a reactor containing 0.1 g-eq of the mononuclear iron complex of trilon B (18.6 g of trilon B and 2.8 g of Fe ³⁺ - molar ratio of 1:1). During the addition, the potential is monitored using a platinum electrode and the content of sulfide ions is monitored using a sulfide-selective electrode (HS-Skr-001). The solution additionally contains a stabilizer - nitrile trimethylene phosphonic acid (NTP) in an amount of 0.01-0.1% of the mass of the absorption solution. The process of adding sodium sulfide is carried out until the potential of the platinum electrode sharply decreases (the Expert-001 device was used) and sulfide ions appear in the solution. At the same time, during the sulfur precipitation process, the residual content of sulfide ions was measured using a sulfide-selective electrode XC-Sкр-001 according to the standard method.

When conducting examples of specific implementation, steel grade ST.10 was used.

The methods used in the measurements are widely known and described, for example by Anufriev N. G., Komarova E. E., Smirnova N. E. Universal corrosion meter for scientific research and industrial control of metal and coating corrosion // Corrosion: materials, protection. 2004, No. 1. P. 42-47; Protective coatings as a method of corrosion inhibition in industry and energy / B. N. Driker, N. V. Tsirulnikova, A. A. Protazanov, N. N. Styagov // Energy saving and water treatment. - 2023. - No. 2 (142). - P. 4-6.

The data are presented in Fig. 1 (change in potential of the platinum electrode).

Absorption solution - a solution of 0.1 g-eq of the iron complex of trilon B (18.6 g/l and 2.8 g/l Fe ²⁺ ).

The corrosion rate was controlled using the Expert-004 device by measuring the polarization resistance. The consumption of Trilon B g/g of sulfur formed was determined by titrating the filtrate with a standard solution of magnesium sulfate using a known method. The amount of sulfur formed was determined by the weight method using a standard method.

Under similar conditions, tests were carried out in accordance with the prototype (see Russian Patent No. 2042403, 1995). The data are given in Table 1.

The obtained data are the average of a series of five parallel determinations. The relative error of the measurement results is ± 5% of the loss of Trilon B and 7% of the corrosion value.

The data presented in Table 1 show that in the presence of NTF as a stabilizer, the losses of Trilon B are reduced and the corrosion rate of structural steel is lowered. This is due to the formation of an insoluble complex of NTF with iron, the solubility of which is 5.5⋅10 ^-4 g/l. The complex is very strong and is used for the quantitative determination of iron even in highly acidic solutions. In this case, the poorly soluble complex formed on the surface of structural steel shields this surface, prevents its further dissolution (corrosion) and, as a result, reduces the consumption of Trilon B as a result of adsorption on newly formed iron hydroxide. A decrease in the concentration of NTF to less than 0.01% (Example No. 3 - 0.005% NTF) worsens the indicators of both the corrosion rate and the consumption of Trilon B per gram of formed sulfur, obviously due to an insufficient rate of formation of the protective film and its thickness. Increasing the concentration of NTF above 0.1% (Example No. 7 - 0.2% NTF) has a negative effect on the specific consumption of Trilon B per gram of sulfur formed. Data on the change in the corrosion value over time at different concentrations are presented in Fig. 2 (change in the corrosion value over time at different dosages of the stabilizer - NTF).

From the presented data it is evident that the use of NTF as a stabilizer affects not only the amount of adsorption, but also the rate of formation of a protective film on the metal surface, ensuring the achievement of the stated technical result.

Table 1

The influence of the stabilizer on the water purification process

p№ Content of stabilizer from the mass of the absorption solution, % Losses
Trilon B, g/g of sulfur formed Corrosion rate, mm/year 1 Test example without stabilizer) 0.25 12 2 Prototype: di-triethyleneamine mixture (1:3), 25g/l 0.09 0.08 3 NTF-0.005 0.12 0.15 4 NTF-0.01 0.08 0.07 5 NTF-0.05 0.075 0.06 6 NTF-0.1 0.07 0.055 7 NTF-0.2 0.09 0.06

Claims (1)

A method for purifying wastewater from sulfides, including the interaction of an iron complex with ethylenediaminetetraacetate and a stabilizer with water containing sulfide ions, characterized in that nitrilotrimethylenephosphonic acid is used as a stabilizer in an amount of 0.01-0.1% of the mass of the absorption solution.