FI107788B - Recycling of heavy metals in waste treatment - Google Patents

Description

107788 RECOVERY OF HEAVY METALS IN WASTE TREATMENT

The invention relates to a process for the recovery and / or recycling of heavy metal as defined in the preamble of claim 1 in connection with the incineration of wood waste treated with a wood preservative.

Heavy metal, as used herein, is understood to mean an element with a density greater than 5 kg / dm 3 which is considered to have a deleterious effect on the environment, humans and / or animals, eg As, Cu and Cr.

The pressure impregnated so. In recent years, economical, easy-to-use and environmentally friendly treatment methods have been sought to treat wood waste impregnated with wood preservative.

15 Surface wood of pressure impregnated wood typically contains about 3 to 24 kg / m3 of impregnating agent and no impregnating agent in the core. The composition of the impregnating agent may be, for example, 13.7% CuO, 34.2% CrO3 and 24.1% As2O3. Alternatively, the wood preservative may comprise e.g.

2 0 of the following components: CuSO 4 · 5 H 2 O, Na 2 Cr 2 O 7 · 2 H 2 O and As 2 O 5 · H 2 O. The composition of the impregnating agent may be in accordance with the AWPA or BS standard. The proportions of the ingredients in the various impregnating agents vary.

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Methods for treating pressurized wood with pressurized wood, such as by extracting • • · *. # Ί · annual metals from wood, are known in the art. Extraction methods have been found to be difficult to implement because heavy metals • · ·; * · *: are firmly bound to wood.

Further, methods for treating pressure impregnated wood in, for example, a copper smelter are known. Wood waste is crushed and burned in a copper smelting • • atmosphere at high temperature. The problem is to grind wood waste to a grain size less than 10 mm *. In addition, the treatment of wood material in the smelter reduces (·· »35) the smelting capacity.

• · ·. Methods of treating pressure impregnated wood by burning or charring are still known.

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Such methods have been found to be suitable for treating pressure impregnated wood and for separating heavy metals from wood. Of the heavy metals, for example, arsenic evaporates mainly with the flue gases, while copper and chromium remain in the ash. The ash can be led to a smelter, for example. However, the problem has been the recovery of heavy metals without, for example, damaging the environment of flue gases, as heavy metals are difficult to remove. A further problem has been the waste water from flue gas scrubbing 10 containing heavy metals such as arsenic. Separating arsenic from waste water is difficult and expensive.

A problem with commonly known combustion methods is emission control.

The object of the invention is to eliminate the above-mentioned problems and to provide an environmentally friendly method for use in the treatment of pressure impregnated wood. In particular, it is an object of the invention to provide a process for the recovery and / or recycling of heavy metals which is easy to implement.

The process according to the invention is characterized by what is claimed.

The invention is based on the recovery and / or recycling of heavy metals in connection with the incineration of wood waste treated with a wood preservative such that the waste is · · crushed or chipped and burned per se ♦. ** ·. to be incinerated, for example in a gasification or grate-type boiler or fluidized bed boiler, the ash from the incineration is led to a smelter where the heavy metals in the ash are mainly recovered, and the flue gases from the incineration are cooled and purified by separating the flue gas. ♦ ♦ · Stable. According to the invention, the flue gases are cooled, the flue gases are separated from the cooled flue gases · «··. ···. 35 arsenic by washing, arsenic-containing wash water and / or flue gas from flue gas scrubbing • ·:. ·: Contains cooling condensation water 107788 arsenic is oxidized to form oxidant to form a solution containing oxidized arsenic, and the resulting solution or arsenic derived therefrom is used in the process of making a wood-impregnating agent. The washed flue gases are heated and passed through a filter to recover residual arsenic.

The ash from the incineration is kept at a temperature above 800 ° C under oxidizing conditions in the final stage of the incineration to provide the lowest possible arsenic content in the ash. The ash is introduced into a treatment process, e.g. a copper smelter, where the heavy metal or heavy metals, e.g. copper and arsenic, are mainly recovered.

Flue gas 15 refers to all gaseous products resulting from combustion. Flue gases contain many different gaseous components. The term "wash water" as used herein refers to any liquid or mixture of various liquids produced by the purification of gases. The wash water preferably contains almost all of the arsenic evaporated in the combustion.

In one embodiment of the invention, the arsenic contained in the condensation and / or wash water is preferably oxidized with hydrogen peroxide, oxygen, air or whatever. ··· with other oxidizing agents. Oxidation can be carried out, for example, in an autoclave using, for example, iodine or activated carbon as the catalyst.

. ···. Arsenic is present in condensation and / or washing water at oxidation numbers +3 and / or +5. In one embodiment of the invention, the arsenic is oxidized to an arsenic compound, wherein the arsenic is present in an oxidation number of +5, preferably arsenic acid, H3A5O4. The oxidized .4 · solution thus formed is a dilute arsenic acid solution.

The solution formed in one embodiment of the invention is further processed to recover and / or utilize the arsenic.

In one embodiment of the invention, the arsenic is precipitated from the formed solution. In one embodiment, 107788 arsenic is precipitated from the resulting solution in the presence of copper, copper compound, oxidant and / or NaOH. The copper or copper compound may be, for example, copper wire grit, metallic copper, copper-arsenic compound such as Cu3As, copper sulfate compound such as CuSO4 · 5 H2O, or the like. In one embodiment, a large amount of a copper compound such as Cu3As or a copper material such as copper wire grit is charged into the reactor in a stoichiometric ratio, and a lower amount of the oxidized solution, i.e. condensation and / or washing water, and an oxidant, e.g. hydrogen peroxide, to precipitate arsenic from the solution. The reaction is then rapid, i.e.. the reaction rate is high. Multiple single charge charges of a copper compound or copper material can be processed, i. the batch of copper compound or copper material is sufficient for more than one repeated precipitation.

In a preferred embodiment of the invention, arsenic precipitation is obtained into a copper arsenate having the chemical formula Cu 3 (AsO 4) 2 or the like. The precipitated copper arsenate can be easily separated from the solution and can be used, for example, as a wood preservative containing copper, chromium and arsenic. for example in the preparation of CCA wood preservative, working solution or concentrate. The residual arsenic solution · · can be precipitated with ferrosulphate and lime.

• · · - *. ···. In one embodiment of the invention, the arsenic-containing solution is concentrated by evaporation.

In one embodiment of the invention, copper, chromium and / or arsenic compounds, e.g., CuO, CrO3, H3A5O4, are added to the arsenic-containing solution and / or precipitate.

*** * In one embodiment of the invention, the arsenic, the arsenic compound, the arsenic-containing solution and / or the arsenic-containing precipitate is passed to a process for the preparation of a wood preservative, e.g., a * 35 * CCA wood preservative. saturated with CCA working solution and / or »· jj; to form a commercial concentrated CCA concentrate, or CCA wood preservative or similar 107788 CCA paste contains arsenic, copper and chromium compounds, preferably e.g. CuO, CrO 3 / H 3 AsSO 4, CuSO 4 5 H 2 O and Na 2 Cr 2 O 7 · 2. H20. The concentration and viscosity of the CCA paste are higher than that of the CCA concentrate.

In one embodiment of the invention, the flue gases are cooled to a temperature of 200-300 ° C while recovering the heat. At this temperature, the partial pressure of the arsenic, As203, in the gas is so high that it does not fray on the surface of the heat recovery apparatus. The cooled flue gases are introduced into a wet scrubber known per se, e.g. an Imatra venturi scrubber, to separate particulate and / or gaseous impurities from the flue gases. The wet scrubber may preferably include a separation chamber, e.g., a cyclone, in which the gas is separated from the scrubbing water. In a wet scrubber, the flue gas is further cooled, for example, to about 40-60 ° C. The scrubbed gas exiting the wet scrubber is heated to 5-40 ° C, preferably 10 -25 ° C, e.g., with a heat exchanger, e.g., about 50-90 ° C, and passed through a gas filter known per se, e.g., a bag filter, to filter for residual impurities. In the filter, the gas passes, for example, through a filter cloth, which is cleaned at certain intervals, for example, by dissolving the impurities that have accumulated there. This solution containing. * · *; eg soluble arsenic can be utilized in wood •. ···. in the manufacture of a lubricant. Of course, any particulate and gaseous separator or filter may be used in the process.

In a wet scrubber, an effective contact surface is provided between the flue gas and the water droplets «· *, whereby the particles and droplets agglomerate to be Ien separable from gas. Wet scrubber, especially Russian ···. 35, also efficiently separates small · · ** 'particulate and gaseous impurities from the gas.

• · • · · · · · · · · · · · · · · · · · · ··· 6 107788

Thanks to the process of the invention, complete recycling of heavy metals such as copper, chromium and arsenic, e.g.

5 In this case the emissions are low and the waste recovery rate is high. The process of the invention incinerates the waste to recover energy, cleans and / or stabilizes the combustion ash, cleans the flue gases from particulate and gaseous impurities, and cleans and / or recovers the condensation water from flue gas cooling and the flue gas cleaning. Heavy metals recovered at various stages, in particular copper and arsenic, can be utilized in the preparation of wood-15 impregnating agent.

The environmental friendliness of the method is a great asset, especially as environmental laws and emission limits continue to tighten.

In the treatment of condensation and / or washing water, the syn-20 solution can be utilized, for example, in the preparation of wood preservative, whereby no waste water is generated. On the other hand, arsenic can be recovered from solution and recycled to make wood preservative, *: * whereby the waste water is substantially pure.

The invention discloses an important alternative for the utilization of wood treated with wood preservative, · · ·. this will reduce the amount of waste wood being landfilled. There is also the benefit of reducing the amount of wood waste that can be classified as hazardous waste, ♦ ♦ · '· * 30, which saves waste costs. The method according to the invention is efficient and easy to implement in connection with existing equipment. The method is inexpensive * · · * for dolls.

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The invention will now be described in more detail with reference to the accompanying drawings, in which the individual embodiments are illustrated with reference to the accompanying drawings, in which Figure 1 illustrates the invention. 2 and 3 illustrate the condensation and / or wash water treatment methods of the invention in the form of a block-5 diagram.

Example 1

The experiment investigated the incineration and recovery of heavy metal emissions of wood waste treated with wood preservative. Wood waste incineration was carried out in a gasifier type boiler to generate heat. The boiler was placed in the hall.

Figure 1 shows a block diagram of treatment of wood impregnated with wood preservative 15 and recovery of harmful substances.

Durable wood waste was chipped into wood chips amounting to 96 solid m3. The wood material contained heavy metal as follows: 20 Cu 0.74 kg / m 3

As 1.04 kg / m3 solid

Cr 1.03 kg / m3 solid

The chips were burned in a boiler. The incineration of wood waste resulted in a total of about 1000 kg of ash containing 25 copper 66 kg, arsenic 30 kg and chromium 99 kg.

. *: *. The ash was fed to the copper smelter where it was ···. were processed together with concentrates. Most of the copper • · e ···. The copper was recovered by copper electrolysis. Chromium and some arsenic were bound to • · · 30. Most of the arsenic was recovered in the form of a Cu3As precipitate upon copper electrolysis. The precipitate was recovered by the method disclosed in • · · US 5141753.

In the manufacture of wood preservative from the Cu3As precipitate, 35 required CCA concentrates are required.

• · • ♦ *! ' Flue gases from combustion were cooled • · j. » ♦ 200-300 ° C and was cleaned in a high pressure fan 8 · 107788 washer. As a result of the cooling of the wash water and the flue gases, the arsenic (3.56 kg / m 3) contained in the condensed condensed water was oxidized with hydrogen peroxide at 50 ° C according to reaction (I). Approximately 95% of the 5 arsenic was found in washing and condensation water at oxidation number +3 (As203) and. the rest at +5 (As2Os).

After oxidation, arsenic was present predominantly at an oxidation rate of +5.

10 As 2 O 3 + 2 H 2 O 2 + H 2 O - ^ 2 H 3 AS 4 O (I)

The arsenic acid resulting from the oxidation and the washing / condensation water formed a dilute arsenic acid solution which could be used as such in the preparation of a wood-borne launcher as a dilute working solution by the addition of copper chromate obtained by mixing CuO and CrO 3. The resulting working solution had a composition of CuO of 2.81 g / dm 3, Cr 3 of 6.76 g / dm 3 and As 2 O 5 of 4.85 g / dm 3. The solution was suitable for use in grade A impregnation according to NTR standards.

Based on the experiment, it was possible to recover arsenic from the flue gases in good yield and in an environmentally friendly manner. Occupational hygiene performed in the hall. ··· measurements showed that workers were not exposed to heavy metals during the experiment.

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EXAMPLE 2 The flue gas flow generated by burning wood preservative treated wood was 5000 Nm / h and its temperature was 1100 ° C. The flue gas contained 5648 kg of dry • - * t ** · gas / m. The water content of the gas was 153 g / kg dry · ** ': gas and the As content was 230 mg / kg dry gas.

··· ^

The flue gas was cooled to 250 ° C by • r * 111 35 indirect cooling and led to a venturi • · **: ** washer where it cooled to 50 ° C. The gas * · · was purged with a venturi scrubber and the washed gas was reheated to about 64 ° C by indirect heating. The water content of the gas was 90 g / kg dry gas and the As203 content was 3 mg / kg dry gas. The gas was passed to a textile filter, where more heavy metals were removed from the gas 5 (Figure 1). After the filter, the gas had an As2 O3 content of 0.04 mg / kg dry gas. Dust emissions and PAHs in the gas were also low.

Over a period of 5 h, 1.95 m3 of condensate and wash water with an average As5 O3 content of 3.55 g / dm3 were collected. The water-containing arsenic was oxidized to arsenic acid as described in Example 1. The solution was concentrated by evaporation to a volume of 1.63 m 3, whereby the solution had an As 2 O 5 concentration of 4.93 g / dm 3.

8.9 kg CuO and 32.1 kg were added to the solution

CrO 3 as described in Example 1. End of solution

volume was 1.75 m3 and the composition of the solution was CuO

5.07 g / dm3, Cr03 18.3 g / dm3 and As205 4.59 g / dm3. No precipitate formed in the solution within 24 h, whereupon the solution was suitable for use in the preparation of a wood preservative as a working solution according to the AWPA standard (P5 type A) containing 28 g / dm3 of metal oxides. The resultant solution can be applied. when diluted, add water to it.

• · «· · *: *: 25 • ·

EXAMPLE 3 By burning of CCA-impregnated wood, condensate was added to 10 dm 3 of inlet / wash water. The condensation water contained As203 3.29 * · ** '30 g / dm3, As205 0.26 g / dm3, Cu2 + 1 mg / dm3 and Cr3 + 0.5 mg / dm3.

** * The solution was oxidized as in Example 1. To the solution was added 77 g of CuSO 4 · 5 H 2 O and 99 g of Na 2 Cr 2 O 7 2 H 2 O. The volume of the solution was 11 dm 3 and the composition was 35 CuSO 4 · 5H 2 O 7.03 g / dm 3, Na 2 Cr 2 O 2 2 H 2 O 8.94 g / dm 3 and • ♦ T As 2 O 5 H 2 O 4.02 g / dm 3. No precipitate formed in solution within 24 h. The solution was suitable for use as a working solution according to BS-··· • * ♦ ♦ ··· 10 107788 standard (4072, part 1, type 2) at a concentration of 20 g / dm 3 in a wood impregnation plant. The corresponding solution can also be used as a dilute or concentrated solution.

5

Example 4

The arsenic (As 2 O 3) in the condensation / wash water was oxidized as in Example 1. The arsenic present in the solution at an oxidation number of 10 +5 was precipitated from the solution according to reaction (II).

AS2O5 + 3 CUSO4 + G NaOH

Cu 3 (AsO 4) 2 + 3 Na 2 SO 4 + 3 H 2 O (II) 15

Arsenic was almost completely precipitated. The resulting Cu3 (As04) 2 precipitate was utilized in the preparation of CCA wood preservative. The residual arsenic was precipitated in a manner known per se, e.g. with ferrosulphate and lime-20a, and by oxidation to give a FeAsO 4 · CaSO 4 precipitate and purified condensation water (Figure 2).

. * t * Example 5 ···· · '· ** 25 • · · ^ • ·: * t *. Figure 2 shows the condensation / wash water. processing method using a block diagram.

• · / ···. Condensed water containing arsenic, 10 dm3, • · »

The As 2 O 3 concentration was 3.55 g / dm 3 and the As 2 O 5 concentration was 0.5 g / dm 3, oxidized at 98 ° C with oxygen to form arsenic acid.

* · '** The solution was passed through a 1 dm3 reactor where it was stirred vigorously. The reactor was filled with 2 kg of shredded copper wire material. Reactor 35 was also fed with 50% hydrogen peroxide at 8 ml / h. Arsenic · T was precipitated according to reaction (III). The temperature during the reaction · · · · * was 55 ° C.

• · · «·» · »·« 11 107788 2 H3As04 + 3 Cu + 3 H202 -> Cu3 (As04) 2 + 6 H20 (III).

The resulting copper arsenate precipitate was removed from the top of the 5 reactors. At this time, the copper wire material remained in the reactor. After precipitation, the pH of the solution was 3.5. With a slight addition of NaOH, the pH of the solution was raised to 5.5. The solution had an arsenic content of 30 mg / dm3 and a copper content of 40 mg / dm3. The final solution 10 was purified as shown in Example 4 and Figure 2, i.e.. the residual arsenic was precipitated.

The copper arsenate precipitate was filtered off. The precipitate was mixed with Cr 3 O and H 3 AsSO 4 to give a concentrated CCA concentrate of 800 g / dm 3 containing 13.7% CuO, 34.2% Cr 3 O and 24.1% As 2 O 5 and 28% H 2 O.

Example 6 Figure 3 shows a block diagram of a method for treating condensation / wash water.

According to Example 1, the oxidized condensate / wash water was fed to a 3 dm3 reactor with

Cu3As precipitate 2 kg. Cu3As precipitate is a waste product produced by: V: 25 as a by-product of the copper industry (Figure 1).

50% hydrogen peroxide 80 was introduced into the reactor. ml at 50 ° C. The Cu3As precipitate was dissolved in acidic acid. condensation / wash water. Arsenic was precipitated by reaction. is according to (IV).

• · · • · * 30

Cu3As + 5.5 H2O2 + H3As04 Cu3 (As04) 2 + 7 H2O (IV) • «·· 9

At the end of the precipitation, a small amount of NaOH was added to the solution, bringing the pH to 5.5. The precipitate was settled at 60 ° C and the clear solution was removed from the reactor. The clear solution had an arsenic content of 30 mg / dm3. The clear solution was capable of being treated as shown in Figure 2. Oxidated condensation / wash water was added to the reactor. The above process steps were repeated so many times that the Cu3As precipitate was almost completely converted to the Cu3 (AsO4) 2 precipitate, which was utilized in the preparation of a concentrated CCA concentrate, paste or working solution of a wood impregnation plant. The same Cu3As precipitate charge could handle several repeated condensation / wash water single charges, e.g. 50-100 x 10 single charges because of the rapid reaction and the stoichiometric excess of Cu3As precipitate relative to arsenic acid.

In all of the above examples, oxygen or air may be used as the oxidizing agent instead of ve-15 peroxide, but at a higher temperature.

The process according to the invention is applicable in various applications for the recovery and / or utilization of various heavy metals, in particular arsenic and copper.

The embodiments of the invention are not limited to the examples given, but may vary within the scope of the appended claims.

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Claims (12)

1. A process for the collection and / or re-use of heavy metals in connection with the incineration of wood waste treated with wood impregnating means, such that the waste is crushed, incinerated by a combustion technique known per se, the ash formed in the incineration is led to a smelters, in which the heavy metals contained in the ash are recovered, and the flue gases formed during combustion are cooled and purified by separating the heavy metals contained in the flue gases, characterized in that the flue gases are cooled, from the cooled flue gases contains, by washing, the arsenic contained in the arsenic-containing wash water formed during washing of the flue gas and / or in the condensed water condensed upon cooling, by means of an oxidizing agent, thereby forming a solution containing oxidized arsenic, and the solution formed The arsenic or arsenic obtained therefrom is used in manufacture The leaching process of a wood impregnating agent, and the washed flue gases are heated and passed through a filter to collect the residue. 2. A process according to claim 1, characterized in that the arsenic contained in the condensation 'V' and / or the wash water is oxidized by means of hydrogen peroxide, oxygen, air or a similar oxide. · Agents. 3. A method according to claim 1 or 2, V * characterized in that the arsenic is oxidized »· ♦ · / · · to an arsenic compound, where the arsenic is present with the oxidation number +5. · * ···· 4. Method according to any of claims 1. ** ·. - 3, characterized in that the arsenic precipitates • M • · # out of the solution formed. • · · * ·· ϊ 35 Process according to any one of claims 1, characterized in that the arsenic is precipitated out of the solution formed in presence of copper, a copper compound, an oxidizing agent and / or NaOH. 6. A process according to any one of claims 1 to 5, characterized in that a copper compound, such as CU3AS, or copper material, such as copper wire chute, is added to the reactor 5 and an oxidized solution and oxidizing agent for precipitating arsenic are discharged from the solution. 7. A process according to any of claims 1 to 6, characterized in that the arsenic precipitates a pure copper senate. Process according to any of claims 1 to 3, characterized in that the arsenic-containing solution is concentrated by evaporation. 15 9. A process according to any one of claims 1 to 8, characterized in that copper, chromium and / or arsenic compounds are added to the arsenic-containing solution and / or the precipitate. Process according to any one of claims 1 to 9, characterized in that the arsenic, the arsenic compound, the ash-containing solution and / or the arsenic-containing precipitate or the like are guided in a process for a wood impregnating agent. to form a use solution, a strong concentrate and / or a paste or the like for the preparation of a wood impregnating agent containing • · · V: copper, chromium and arsenic. 11. A process according to any one of claims 1 to 3 or 8, characterized in that the solution containing oxidized arsenic is added copper and chromium compounds, and it is used as a use solution in a wood impregnation process for ... of a wood impregnating agent containing • · • y * copper, chromium and arsenic. Method according to any of claims 1, characterized in that the flue gases are cooled to a temperature of 200 - 300 ° C, the flue gases. Washes in a washer, where they are cooled to a temperature of 40 - 60 ° C, and the washed flue gases are heated to a temperature of 5 - 40 ° C, advantageously 10 - 25 ° C. , before passing through the filter. · · · · · · ··· · · · · · · · · · · · · · · · · · · · · · · · · · · · 1 · • · «• · · t - ♦ • · • · · • ♦ • 1 · • · · • · · · · · · 1 · · · · · · · · 1 1 • · ♦ · · · · · · · 2