Method for recovery of platinum metal-containing sludge

FIELD: sludge recovery from surface depositions of chemical equipment.

SUBSTANCE: invention relates to method for recovery of sludge containing platinum-group metals from equipment using platinum metal-based catalysts. Method includes treatment with aqueous solution of active chemical agent (e.g. sodium-ammonium-substituted ethylenediaminetetraacetic salts) while controlling pH value and removing sludge retained on treated surface with diluted aqueous solution of mineral salts or mixture thereof. pH value is adjusted at 2-10, preferably at 3-9 by adding of organic acid selected from group containing citric, oxalic, maleic, phthalic, adipic, glutaric, succinic acids or basic agents selected from sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate, and hydrochloric acid, sulfuric acid or phosphoric acid is used as mineral acid.

EFFECT: recovery platinum-group metal with improved yield.

4 cl, 1 tbl, 12 ex

The invention relates to the technology of extracting sludge containing platinum group metals (PGMs)from deposits on the surfaces of equipment of chemical plants using the catalysts containing these metals and losing them in the process of operation.

During long-term operation units, for example, in the production of non-concentrated nitric acid, heat exchange surfaces, the accumulation of IPY by the condensation of vapors of their oxides. At the same time there and on the inner walls of the apparatus are deposited fine particles of sludge containing PGM separated mechanically from the surface of the catalyst gauzes. As a result of significant quantities of PGMs are tubes in boilers, condensers-condensers, Cuba absorption column, the bottoms of storage of finished products.

The method for extracting sludge containing metals of the platinum group of deposits on surfaces of the apparatus installations using platinum catalysts, including the processing of these surfaces with an aqueous solution of the active chemical agent in the presence of circulation of the solution along the surface being cleaned and bubbling air into the treatment zone followed by filtration of the separated sludge from the solution. As the active agent is proposed to use three groups of chemicals, sharply distinguishing the I in its properties: mineral and organic acids, alkalis, amines [RF Patent №2083261, 1996, 22, 11/00].

The disadvantages of this method is the necessity of the use of forced circulation of the active chemical agent in conjunction with air sparging, which complicates the process and increases the corrosion of the base metal. The particle size of the formed sludge is very small, which makes use of to highlight filtering. Some of the used chemicals cause increased corrosion even in the absence of bubbling and circulating. Recommended concentrations of these reagents (3-6%) is too high, which leads to increased their expenditure on treatment.

Closest to the invention is a method for extracting slurry containing platinum group metals from deposits on the surfaces of the apparatus units, using catalysts based on platinum, including first processing deposits with an aqueous solution of the active chemical agent to adjust pH of the medium, and then removing remaining on the treated surfaces of the sludge. As an active chemical agent is used an aqueous solution of fluoride and/or hydrohloride ammonium, pH adjustment in the range of 3-9,5 lead ammonia. To remove the loosened sludge from the treated surface using a sparging or mechanical sobremisana [RF Patent №2188246, 2000, From 22 In 11/00].

N the drawbacks of this method consist in the use of sparging air or mechanical Sobrevivencia, what complicates the cleaning process. The concentration of the active chemical agent is too high 3-5%, which leads to increased consumption of reagents for treatment. Regulation of pH with ammonia is quite difficult, corrosion of the base metal equipment at low pH high, especially in the presence of air sparging. The particle size of the formed sludge is very small, which makes use of to highlight filtering. Processing time the reagent is large (~24 hours).

The present invention is directed to solving the following technical tasks: simplify the extraction process sludge, reduced consumption of reagents, reducing the corrosive effects on the treated surface, reducing processing time while maintaining a high degree of extraction of platinum group metals.

The technical result is achieved by a method of extraction of sludge containing metals of the platinum group of deposits on the surfaces of equipment and piping installations using catalysts based on platinum, including first processing deposits with an aqueous solution of the active chemical agent to adjust pH of the medium, and then removing remaining on the treated surface of the sludge. According to the invention as the active chemical agent use sodium ammonization salt atlantium tetraoxane acid, and removing remaining on the treated surface of the sludge is carried out by treatment with an aqueous solution of diluted mineral acids or mixtures thereof. The adjustment of pH in the region of 2-10, preferably 3-9, carry out the addition of organic acids from the group of citric, oxalic, maleic, phthalic, adipic, glutaric, succinic or alkaline reagents from the group of: caustic soda or caustic potash, carbonate of sodium or potassium, ammonium water. As a mineral acid using hydrochloric, sulfuric, phosphoric acid or mixtures thereof.

Distinctive features of the method according to the present invention lies in the fact that the treatment of the sediments as the active chemical agent use sodium ammonization salt ethylenediaminetetraacetic acid adjusted pH in the region of 2-10, and removing remaining on the treated surface of the sludge is carried out by treatment with an aqueous solution of diluted mineral acids or mixtures thereof.

Additional distinguishing features are that the adjustment of pH in the region of 2-10, preferably 3-9, carry out the addition of organic acids from the group of citric, oxalic, maleic, phthalic, adipic, glutaric, succinic or alkaline reagents from the group caustic soda, caustic potash, sodium carbonate, potassium carbonate. As diluted min the mineral acids used salt, phosphoric, sulfuric, or a mixture thereof.

The present invention meets the condition of patentability - novelty”, as in the prior art failed to find technical solutions, the essential features which would coincide with all the signs in the first independent clause. The present invention meets the condition of patentability - “inventive step”, since the prior art has failed to find technical solutions, the hallmarks of which are aimed at providing the same technical problems, the solution of which the invention is directed.

The essence of the proposed method lies in the fact that when exposed to the sodium and ammonium salts of ethylenediaminetetraacetic acid (EDTA) at pH 2.0 to 10 (preferably 3 to 9) of the dense sludge on the treated surface are removed, mainly ions of Fe³⁺, Fe²⁺at pH 2.0-7 and/or mainly ions of Al, Si, Mg, Ca at pH 7-10, thick residue on the cleaned surface acquires a special structure and subsequent short-term exposure to concentrated solution of mineral acid leads to swift detachment in the form of flakes. This flaking particles have a relatively large size, which makes use of filtering is not needed, because they almost immediately settle to the bottom of cleansing the constituent unit. The nature of the reagents, as well as lack of circulation and bubbling dramatically reduce corrosion. The processing time of the active reagent is reduced by 2-4 times (on average, three times).

The invention is illustrated by the following examples.

Example 1. The outer surface of the tube bundles economizer installation of diluted nitric acid production by the so-called combined scheme, which are thick black deposits of Fe₂O₃+Fe₂About₃·1,2 H₂About 50 g/m²containing 9.5% of the PGM process 5 hours with an aqueous solution containing 0,55% 2N-substituted salts of EDTA and 0.35% maleic acid. the pH of the solution during the course of treatment varies from 3.0 to 6.0. After processing the pipe heater for 20 minutes immersed in 4%aqueous solution of hydrochloric acid, which is accompanied by the almost complete destruction of the remaining sludge from treated surfaces (almost 100%removal of sludge from smooth surfaces). Removing PGM - 98,1%. The PGM content in the spent solution is less than 1 mg/L. Traces of corrosion on the basic material and welds not found.

Example 2. The outer surface of the tube bundles of the economizer, which are deposits of oxides of divalent or trivalent iron, 9.5% of the IPY, and -10% of compounds of Si and Al (trapped in deposits of refractory lining), obrabecim the Ute 6 hours with an aqueous solution, containing 0.35% of 4N-substituted EDTA, prepared by dissolving EDTA in aqueous solution of sodium carbonate. The initial pH of the solution of 4-substituted EDTA at the beginning of treatment equal to 9.2 at the end of the processing pH 7.5. After processing the pipe heater for 20 minutes immersed in 4%aqueous solution of hydrochloric acid, which is accompanied by the almost complete destruction of the remaining sludge from treated surfaces. Removing PGM - 97,0%, the content of platinum group metals in the spent solution of 2 mg/L. No corrosion of the base metal and welded joints of pipes.

Examples 3-9 are summarized in table 1.

Example 10 (the prototype). The outer surface of the tube bundles of the economizer from example 1 is treated for 24 hours with an aqueous solution containing 4% of NH₄F at pH 3.0, while air flow through the impeller is placed under the pipe heater. At the end of the process the solution is filtered, separating crumbled sludge. The degree of extraction of PGMs is 97%. Corrosion of welds lined x-ray analysis.

Example 11 are summarized in table 1.

Set in the present invention, the technical problems are solved only with the observance of the processing sequence including a first processing deposits in an aqueous solution of sodium ammonization salt of EDTA in the claimed period of pH, and then removing remaining on the treated surface by semirestored diluted mineral acids. When changing this sequence on the back of the main positive effect is a high degree of extraction of PGM - drops, which is evident from the following example.

Example 12. The pipe heater with sediments from example 1 is treated first with 4%Hcl solution for 20 minutes, and then for 6 hours with an aqueous solution containing 0,55% 2N-substituted EDTA. The degree of surface cleaning 40-50%, and the degree of extraction of PGM - 25%.

Considering the above examples are obvious advantages of the proposed method for extracting sludge containing PGM compared with the known, namely:

1. Practically no corrosion at high efficiency extraction of PGM, which makes possible the repeated execution of the following operations on the same hardware.

2. The simplification of the processing result from the elimination of the purification technology-intensive and not always available at the work site operations circulation sparging and filtration.

3. Low consumption of reagents: the concentration of the active agent and organic acids do not exceed 1%.

4. A significant reduction in processing time.

It should be noted that the recommended range of initial pH of the working solution due to the increase in corrosion testing of pipes at pH<3 and increased losses of PGM with worked solutions at pH outside the range 2-9.

The high efficiency of the process, is explained by the selective effect of the active chemical agent in the respective ranges of pH values on individual items included in a thick residue on the treated surface. The result of such exposure dense precipitate is riddled with numerous thin cross-cutting channels through which mineral acid reaches the surface of the base metal, resulting in rapid removal of this sediment in the form of relatively large scales.

1. The method for extracting slurry containing platinum group metals from deposits on the surfaces of the apparatus units, using catalysts based on platinum, including processing deposits with an aqueous solution of the active chemical agent to adjust the pH of the environment and the subsequent destruction of remaining on the treated surface of the slurry, characterized in that the treatment of the sediments as the active chemical agent use sodium-substituted ammonium salts of ethylenediaminetetraacetic acid adjusted pH in the region of 2-10, and removing remaining on the surfaces of the sludge is carried out by treatment with an aqueous solution of diluted mineral acids or mixtures thereof.

2. The method according to claim 1, characterized in that the adjustment of pH is carried out in the field 3-9.

3. The method according to claim 1 or 2, characterized in that the adjustment of the pH is performed by adding an organic acid from the group of citric, oxalic, maleic, phthalic, adipic, glutaric, succinic or alkaline reagents from the group of: caustic soda, caustic potash, sodium carbonate, potassium carbonate.

4. The method according to claim 1, characterized in that the mineral KIS is from the use of salt, phosphoric, sulfuric.