RU2282598C1 - Method for chemical stabilization of galvanic sludges being for long time on storage - Google Patents

Abstract

FIELD: chemical detoxification methods.

SUBSTANCE: invention relates to methods for chemical detoxification of stored for long time (at least two years) galvanic production effluent sediments and can be used in mechanical and instrumentation engineering as well as in electronic industry. In the beginning of process, galvanic sludges are activated with sulfuric acid solution, pH 3.8-4.0, for 15-20 min, after which, ferritized galvanic sludge, ferrous sulfate, and alkali to pH 9-10 are added at stirring and heating. Ferritizing process is performed for 25-30 min while maintaining temperature of reaction mixture heating to 50-60^°C.

EFFECT: enabled detoxification of long-term galvanic sludges and reduced detoxification expenses.

1 dwg, 3 tbl

Description

The invention relates to methods for chemical treatment of wastewater sludge from galvanic plants, stored for a long time (two years or more), and can be used in machine, instrument-making, and electronic industries.

A known method of disposal of sludge from galvanic plants according to the USSR AS 1693098, MKI 5 C 22 B 7/00, according to which the sludge is mixed with sludge from oil-containing wastewater at a ratio of 1: (0.15-1). The resulting mixture is fired at a temperature of 1000-1200 ° C, the resulting mass is crushed and leached with sulfuric acid. After leaching, the solution is filtered, while the precipitate contains compounds of calcium oxide with silicon oxide, chromium silicate, and metals that are in the form of sulfates in the solution are isolated in the form of hydroxides by fractional crystallization with increasing pH to 10.

The disadvantages of this method include the introduction into the process of the operation of firing at a temperature of 1000-1200 ° C, which leads to the sublimation of metals such as zinc, cadmium, etc., the formation of benzpyrene due to thermal decomposition of the organic component of the precipitation of oil-containing wastewater. In addition, the separation of metals in the form of hydroxides by fractional crystallization does not allow the separation of metals, since due to adsorption or due to the fact that the pH hydration regions for many heavy metals overlap, they are coprecipitated.

A known method of stabilizing suspensions of galvanic sludge by ferritization according to the patent of the Russian Federation 2116978, C 02 F 11/00. According to the method, a water-soluble ferrous salt of ferrous element (ferritizing element) is introduced into the suspension with the stirrer operating in the amount of 0.06-0.08 per unit solid phase of the suspension, then alkali to pH 9-10, the mixture is heated to 70-80 ° C at a speed 3-4 ° C / min. These conditions in the absence of expensive ferritization catalysts and an oxidizing agent contribute to the formation of a reliable ferrite shell on particles of heavy metal hydroxides. However, the method requires large energy consumption for heating the suspension.

The closest in number of similar features is the method of precipitation ferritization (Dykhanov N.N. et al. On the issue of chemical stabilization of precipitation generated in wastewater treatment processes // Sat Ecological problems in galvanic production: seminar materials, 1992. - M .: TsRDZ, 1992, p.135). According to this method, the settled precipitate is mixed with alkali to a pH of 9-10 with a ferritization catalyst, a water-soluble salt of iron (II) is introduced, the mixture is heated to 70-90 ° C and, at the final stage, the mixture is bubbled with air. The purpose of the water-soluble iron (II) salt is that during its hydrolysis, Fe ²⁺ ions appear in the reaction medium, as well as a strong inorganic acid, which partially dissolves the heavy metal hydroxides contained in the sludge, as a result of which heavy metal cations appear in the mixture (Me ²⁺ ). When this reaction mixture is alkalized to pH 9-10, mixed hydroxides (Me _n Fe _3-n (ОН) ₆ ) are formed, and their subsequent oxidation with atmospheric oxygen produces heavy metal ferrites (MeO * Fe ₂ О ₃ ). The total reaction of the ferritization process described in the prototype is as follows:

Me (OH) ₂ + 2Fe (OH) ₂ + 1 / 2O _{2 (air)} → MeO · Fe ₂ О ₃ + 3Н ₂ O

The disadvantages of the prototype include large energy consumption for heating the mixture in the reactor; the use of expensive and scarce auxiliary materials, which then need to be processed, which generally complicates the technology of sludge ferritization. Experimental studies show that the degree of neutralization of suspensions of freshly formed sludge is within the established standards, however, the neutralization of sludges that have been stored for a long time using this method is not effective without their preliminary activation.

These disadvantages are eliminated by the proposed technical solution.

The objective of the invention is the creation of a method for the chemical stabilization of galvanic sludge stored for a long time, including the preliminary activation of metal hydroxides contained in the sludge, as well as reducing the cost of the ferritization process by lowering the temperature and refusing auxiliary expensive materials.

The technical result is the ability to neutralize galvanic sludge stored for a long time, receive practically non-toxic waste (hazard class V), which do not require specialized toxic industrial waste landfills, and reduce the cost of their disposal.

To achieve a technical result, a method for the chemical stabilization of suspensions of galvanic sludge that has been stored for a long time is claimed, comprising mixing a suspension of galvanic sludge with ferrous sulfate and alkali to a pH of 9-10, heating the mixture in a reactor, and ending the process by bubbling the mixture with air.

The peculiarity is that at the beginning of the process galvanic sludge, which are stored for a long time, are activated with a solution of sulfuric acid with a pH of 3.8-4.0 for 15-20 minutes, after which a ferritized slurry is introduced into the suspension with stirring and heating, the ferritization process is carried out for 25-30 minutes and the reaction mixture should be heated to 50-60 ° C.

The invention is illustrated by the technological scheme of the ferritization process shown in the drawing, where 1 is a ferritization reactor; 2 - mixer; 3 - level glass; 4 - pH meter; 5 - thermometer; 6, 7 - containers with solutions of iron (II) sulfate and sodium hydroxide; 8 - rotameter; 9 - pump; 10 - vacuum filter; 11 - device for washing sludge; 12 - a knife for removing sludge from the drum of the vacuum filter 10; B ₁ ... B ₉ - valves.

Information confirming the possibility of carrying out the invention with obtaining the above technical result are as follows.

The method of chemical stabilization of galvanic sludge, stored for a long time, it is advisable to carry out as follows.

The ferritization reactor 1, with the valve B ₁ open, is filled to 1/2 of the working volume with process water. Then, with the working mixer 2, the calculated amount of galvanic sludge from the sludge collector is introduced into it. To activate the slurry suspension with an open valve B _2, an acid solution is introduced to a pH of 3.8-4.0 and the resulting mixture is stirred with a stirrer 2 for 15-20 minutes.

Then, steam is fed into the ferritization reactor 1 with the open valve B7 and the mixture is heated with stirring to a temperature of 30-35 ° C (the temperature is controlled by thermometer 5). Then, a seed — a ferritized galvanic sludge — is introduced into the reaction mixture as a product of the previous process of chemical stabilization of the sludge in an amount of 10% by weight of the suspension in the reactor. Within 5-8 minutes of mixing, the mixture is homogenized. In a homogenized mixture with open valve B _5, ferrous sulfate is introduced from tank 6 from the calculation: the ratio of the mass of Fe (II) ions to the mass of the solid phase of the suspension is 0.06-0.12. This allows you to get environmentally friendly products without reagent overruns. Then, in the mixture with the open valve B ₆ from the tank 7, add a 20% alkali solution to a pH of 9-10, controlling the pH of the reaction mixture using a pH meter 4. After the introduction of the reagents, the mixture is heated with stirring to a temperature of 50-60 ° C.

When this temperature is reached, compressed air is supplied to the reaction mixture with valve B ₈ open and sparging is carried out with a volume flow of 2.5-3 cubic meters. m per cubic meter m of suspension (air flow is monitored using a rotameter 8) for the oxidation of excess Fe (II) ions and the conversion of a mixture of heavy metal hydroxides into ferrites.

Thus, the process of ferritization of galvanic sludge proceeds in two stages:

1. When alkalizing the reaction mixture containing heavy metal cations (Me ²⁺ ) formed during acid activation of the sludge and Fe ^{2+ ions} formed during the hydrolysis of iron (II) sulfate, mixed hydroxides (Me _n Fe _3-n (ОН) are formed ) ₆ ) according to the reaction:

_(3-n) Fe ²⁺ + _n Me ²⁺ + 6OH ^- → Me _n Fe _3-n (OH) ₆

2. upon subsequent oxidation of the mixture with atmospheric oxygen, ferrites of heavy metals (Me _n Fe _3-n O ₄ ) are formed by the reaction:

Me _n Fe _3-n (OH) ₆ + _^1/2 O ₂ → Me _n Fe _3-n O ₄ + 3H ₂ O

When the time of bubbling slurry ferritizirovannyh galvanic sludge at the open valve V ₉ via pump 9 is fed on the suction filter 10 for dewatering and washing. Sludge washing is carried out using device 11. The resulting filtrate and washing water are returned to the neutralization stage of the galvanic drains, and the dehydrated and decontaminated sludge is taken out for disposal.

The degree of neutralization of ferritized galvanic sludge is determined by calculating their hazard class according to a standard method using data on the content of heavy metal ions in an aqueous extract, which is prepared according to GOST 26423-85.

An example implementation of the method.

Experimental studies were conducted on a pilot installation of 10 liters. A 20% solution of sulfuric acid was used as a reagent for acid activation of galvanic sludge, a 10% solution of iron (II) sulfate calculated on anhydrous salt was used as a ferritizing reagent, and a 20% sodium hydroxide solution was used as an alkaline reagent. The choice of mass fractions of dissolved substances in these solutions is due to the fact that the preparation of more concentrated solutions under production conditions is associated with certain technological difficulties, and the use of less concentrated solutions leads to a significant dilution of the reaction mixture, an increase in its volume, and, accordingly, an increase in the size of the ferritization reactor. The moisture content of the galvanic sludge suspension obtained in the reactor was about 95%. The gross content of heavy metals in the galvanic sludge of the two enterprises used to study the ferritization process is shown in table 1.

Table 1
Gross metal content in galvanic sludge Metal Copper Nickel Zinc Chromium Lead Cadmium The metal content in the sludge, mg / kg No. 1 4122.5 446.0 8860.2 34520.7 417.4 - Number 2 1284.5 3240,0 4125.6 8718.5 365,2 1123.0

The results of studies on optimizing the main parameters of the ferritization process are shown in Table 2. Two metals were selected as the controlled toxic components of galvanic sludge - the main and amphoteric ones with the maximum content in the sludge: for sludge No. 1 - copper and chromium, for sludge No. 2 - nickel and chromium.

table 2
Leaching of heavy metal ions from ferritic galvanic sludge (FGS) obtained at different values of the controlled process parameters Indicator Indicator value The concentration of metal in an aqueous extract of ferritized galvanic sludge, mg / l FSH №1 FSH №2 Cu Cr Ni Cr 1. pH of the solution for the activation of galvanic sludge 3,7 0.11 0.40 0.05 0.32 3.8 0.08 0.26 0.05 0.22 3.9 0.10 0.36 0.08 0.30 4.0 0.28 0.43 0,03 0.40 4.1 1.18 2,32 0.09 1.13 2. The time of the activation process, min 10 1.94 8.16 1,03 4,56 fifteen 0.12 0.22 0,07 0.41 twenty 0.04 0.13 0.06 0.28 25 0,03 0.18 0.06 0.32 3. The ratio of the mass of Fe ²⁺ to the mass of the solid phase of the suspension 0.05 2.24 3.16 0.63 1.81 0.06 0.17 0.23 0.09 0.35 0.10 0.22 0.18 0.09 0.16 0.12 0.68 0.41 0.10 0.30 0.13 0.35 0.46 0.09 0.28 4. The temperature of the reaction mixture, ° C 45 1.68 2.44 1.42 1.26 fifty 0.80 0.28 0.05 0.40 55 0.12 0.08 0.01 0.16 60 0.08 0.10 0,03 0.20 65 0.06 0.13 0,03 0.18 5. pH of the reaction mixture 8 1.12 1.36 0.82 1.29 9 0.09 0.25 0.10 0.31 10 0.02 0.08 0.01 0.16 eleven 0,07 0.73 0.02 0.87 6. The time of the ferritization process, min twenty 1,08 0.64 0.08 1.17 25 0.06 0.09 0.06 0.38 thirty 0.02 0.14 0.01 0.16 35 0,03 0.15 0.02 0.24 MAC of metal in drinking water, mg / l 1,0 0.5 0.1 0.5

The studies performed allowed us to identify the interval of the main parameters of the ferritization process, which ensures reliable neutralization of galvanic sludge stored for a long time:

- pH of the solution for the activation of galvanic sludge 3.8-4.0;

- time of the activation process, min 15-20;

- the ratio of the mass of Fe ²⁺ to the mass of the solid phase of the suspension of 0.06-0.12;

- the temperature of the reaction mixture, ° C 50-60;

- pH of the reaction mixture is 9-10;

- the time of the ferritization process, min 25-30.

Table 3 shows the results of comparative studies on the disposal of sludge from two enterprises, which have been stored for a long time, by ferritization with and without acid activation (experiments were carried out at certain optimal values of the main parameters of the activation and ferritization processes).

Table 3
Leachability of heavy metal ions from FGS obtained with and without acid activation: pH of the solution for sludge activation - 3.9; activation process time - 20 min;
m _Fe ²⁺ / m of the _{solid phase of the suspension} is 0.1; the temperature of the reaction mixture is 55 ° C; the pH of the reaction mixture is 9.5; ferritization process time - 30 min Metal The concentration of metal in an aqueous extract of ferritized galvanic sludge, mg / l MAC of metal in drinking water, mg / l FSH №1 FSH №2 with acid activation without activation with acid activation without activation Cu 0.02 2.67 0.05 3.42 1.00 Ni 0,03 2,39 0.01 3.08 0.10 Zn 0.15 4.18 0,07 3.76 1.00 Cr 0.08 8.59 0.16 4.11 0.50 Pb 0.00 2.64 0.00 2.16 0,03 Cd - - 0.00 1.85 0.01

Analysis of aqueous extracts from ferritized galvanic sludges obtained without the use of acid activation showed that the content of heavy metal ions in them significantly exceeds the maximum permissible concentration for drinking water. An increase in the time of the ferritization process, temperature, pH, and consumption of iron (II) sulfate practically did not affect the degree of neutralization of galvanic sludge that has been stored for a long time. Thus, it has been experimentally established that without activation of galvanic sludges that have been stored for a long time, their neutralization by ferritization does not occur.

The proposed method for the chemical stabilization of galvanic sludge, which has been stored for a long time, is of considerable interest to the national economy, since in many enterprises, in addition to the problem of neutralizing freshly formed galvanic sludge, the problem of eliminating already accumulated old sludge is very acute.

The proposed technology has received positive conclusions from the Center for State Sanitary and Epidemiological Supervision of Ulyanovsk and the expert commission of the State Ecological Expertise Department of the State Unitary Administration of the Ministry of Natural Resources of the Russian Federation in the Ulyanovsk Region and is recommended for implementation at one of the city’s enterprises.

Claims (1)

The method of chemical stabilization of galvanic sludge stored for a long time, including mixing a suspension of galvanic sludge with ferrous sulfate and alkali to a pH of 9-10, heating the mixture in a reactor and at the end of the process sparging the mixture with air, characterized in that at the beginning of the process, activation galvanic sludge with a solution of sulfuric acid with a pH of 3.8-4.0 for 15-20 minutes, after which a ferritized galvanic sludge is introduced into the suspension with stirring and heating, the ferritization process is exist for 25-30 minutes and the reaction mixture should be heated to 50-60 ° C.