Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/46—Removing components of defined structure
  • B01D53/64—Heavy metals or compounds thereof, e.g. mercury
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B30/00—Obtaining antimony, arsenic or bismuth
  • C22B30/04—Obtaining arsenic
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/001—Dry processes
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/722—Oxidation by peroxides
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/725—Treatment of water, waste water, or sewage by oxidation by catalytic oxidation
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/72—Treatment of water, waste water, or sewage by oxidation
  • C02F1/74—Treatment of water, waste water, or sewage by oxidation with air
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/103—Arsenic compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2101/00—Nature of the contaminant
  • C02F2101/10—Inorganic compounds
  • C02F2101/20—Heavy metals or heavy metal compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/18—Nature of the water, waste water, sewage or sludge to be treated from the purification of gaseous effluents
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to a method as defined in the preamble of claim 1 for the recovery and/or recirculation of heavy metal in conjunction with the combustion of waste wood treated with a wood preservative .
• 'heavy metal 1 refers to an element having a density exceeding 5 kg/dm 3 and regarded as having a detrimental effect on the environ- ment , humans or animals if encountered in excessive concentrations, e.g. As, Cu and Cr .
• the amount of impregnating agent in the sap- wood portion of pressure- impregnated wood is typically about 3 - 24 kg/m 3 while the heartwood portion con- tains no impregnating agent.
• the composition of the impregnating agent may be e.g. 13.7 % CuO, 34.2 % Cr0 3 and 24.1 % As 2 0 5 .
• the wood preservative may alternatively consist of e.g. the following components: CuS0 4 • 5 H 2 0, Na 2 Cr 2 0 7 • 2 H 2 0 and As 2 0 5 • H 2 0.
• the composi- tion of the wood preservative may be as defined in the AWPA or the BS standard. The proportions of different substances in different wood preservatives vary.
• the object of the invention is to eliminate the problems referred to above and to disclose an environmentally friendly method for use in the treatment of pressure-impregnated wood.
• a specific object of the invention is to disclose a method for the recovery and/or recirculation of heavy metals that is easy to implement .
• the invention is based on recovering and/or recirculating heavy metals in conjunction with combustion of wood residue treated with a wood preservative, by crushing, e.g. chipping, and burning the wood resi- due by a combustion technique known in itself, e.g. in a gasification or grate type boiler or in a fluidized bed boiler.
• the ashes produced in the combustion proc- ess are passed into a smelter, where most of the heavy metal or heavy metals present in the ashes is recovered, and the combustion gases produced in the combustion process are cooled down and/or purified by sepa- rating the heavy metals contained in the combustion gases.
• the combustion gases are cooled down, arsenic contained in the combustion gases is separated from the cooled combustion gases by washing, i.e. by absorbing the arsenic into water.
• the arsenic contained in the arseniferous wash water produced by the washing process of the combustion gases and/or in the arseniferous condensation water condensed in a simultaneous cooling process is oxidized by using an oxidizing agent, thus producing a solution containing oxidized arsenic.
• the solution produced is treated so as to allow the solution and/or arsenic to be utilized in a wood preservative manufacturing process.
• the washed combustion gases are heated again and passed through a filter to recover the re- sidual arsenic.
• the ashes produced in the combustion process are exposed in the last stage of the process to oxidative conditions at a temperature of over 800 °C, thus minimizing the arsenic content of the ashes.
• the ashes are passed into a treatment process, e.g. into a copper smelter, where most of the heavy metal or heavy metals, e.g. copper and arsenic, is recovered.
• 'combustion gases' refers to all gaseous products appearing in conjunction with the combustion.
• the combustion gases contain various gaseous components.
• 'Wash water 1 in this context means any liquid or mixture of different liquids that is produced in the purification of the gases.
• the wash water preferably contains almost all of the arsenic evaporated in the combustion process.
• the arsenic contained in the condensation water and/or wash water is oxidized, preferably using hydrogen peroxide, oxygen, air or any other oxidizer. Oxidization by means of oxygen can be accomplished e.g. in an autoclave by using e.g. iodine or active carbon as a catalyst .
• Arsenic occurs in the condensation water and/or wash water with a valence of +3 and/or +5.
• the arsenic is oxidized to produce an arsenic compound in which arsenic occurs with a valence of +5, preferably arsenic acid, H 3 As0 4 .
• the oxidized solution produced is a weak arsenic acid solution.
• the arsenic is precipitated from the solution produced.
• the arsenic is precipitated from the solution in the presence of copper, a copper compound, an oxidizer and/or NaOH.
• the copper or copper compound may consist of e.g. crushed copper wire, metallic copper, a copper-arsenic compound, such as Cu 3 As, a copper sulfate compound, such as CuS0 4 • 5 H 2 0, or the like.
• the reaction is a rapid one, i.e. the reaction rate is high.
• a single charge of copper compound or copper material can be used to treat several batches of solution, in other words, a single copper compound or copper material charge is sufficient for several repeated precipitation treatments .
• precipitation of arsenic into copper arsenate the chemical formula for which is Cu 3 (As0 ) 2 or equivalent.
• the precipitated copper arsenate can be easily separated from the solution, and it can be utilized e.g. in the preparation of a CCA working solution or a CCA concentrate.
• the residual arsenic in the solution can be precipitated using ferrous sulfate and calcium.
• the arseniferous solution is concentrated by evaporation.
• copper, chromium and/or arsenic compounds e.g. CuO, Cr0 3 , H 3 As0 4 , are added into the arseniferous solution and/or precipitate.
• the arsenic, arsenic compound, arseniferous solution and/or arseniferous precipitate or the like are/is passed into a manufacturing process for the production of e.g. a commercial wood preservative to form a CCA working solution, a strong CCA concentrate and/or CCA paste or the like.
• a CCA wood preservative contains arsenic, copper and chromium compounds, preferably e.g. CuO, Cr0 3 , H 3 As0 4 , CuS0 4 ⁇ 5 H 2 0 ja Na 2 Cr 2 0 7 • 2 H 2 0.
• concentration and viscosity of CCA paste are higher than those of CCA concentrate.
• copper and chromium compounds are added into the solution containing oxidized arsenic, and the solution is utilized as a CCA working solution in a wood impregnating process .
• the com- bustion gases are cooled down to a temperature of 200
• the cooled combustion gases are passed into a wet gas washing apparatus known in itself, e.g. an Imatra Venturi washer, to separate particles and/or gaseous impurities from the combustion gases.
• the wet washing apparatus may preferably comprise a separating chamber, e.g. a cyclone, in which the gas is separated from the wash water.
• the combus- tion gases are cooled further to about 40 - 60 °C .
• the temperature of the washed gas coming out of the wet washing apparatus is raised by 5 - 40 °C, preferably 10 - 25 °C, e.g. by means of a heat exchanger e.g. to a level of 50 - 90 °C and the gas is passed through a gas filter known in itself, e.g. a bag filter, to filter out the residual impurities.
• a gas filter known in itself, e.g. a bag filter, to filter out the residual impurities.
• the gas passes e.g. through a filter cloth which is cleaned at certain intervals e.g. by dissolving the impurities gathered in it.
• the solution used which contains e.g. soluble arsenic, can be utilized in the manufacture of a wood preservative.
• any device or filter for the separation of corpuscular or gaseous impurities can be used in the method.
• the wet washing apparatus In the wet washing apparatus, an effective contact area between the combustion gas and the water drops is achieved, with the result that the particles and drops agglomerate and can therefore be separated from the gas.
• the wet washing apparatus especially a Venturi washer, effectively separates even small cor- puscular and gaseous impurities from the gas.
• the method of the invention makes it possible to achieve a perfect recirculation of heavy metals, such as copper, chromium and arsenic, contained e.g. in a wood preservative, without producing environ- mental stress. This means a low level of emissions and a high degree of utilization of the waste. Further, the energy contained in wood residue treated with a wood preservative can be recovered and the heavy metals, such as arsenic, contained in the wood residue can be effectively recirculated.
• heavy metals such as copper, chromium and arsenic
• the wood residue is burned to recover the energy, the ashes produced in the combustion process are cleaned and/or stabilized, the combustion gases are cleansed of corpuscular and gaseous impurities and the condensation water produced in the process for cooling the combustion gases as well as the wash water produced in the purification of the combustion gases is purified and/or utilized.
• the heavy metals, especially copper and arsenic, recovered in different stages of treatment can be utilized in the production of a wood preservative.
• the environmentally friendly nature of the method is a great advantage, especially as the environmental laws and restrictions on emissions are continuously becoming stricter.
• the solution produced in the treatment of condensation water and/or wash water can be utilized e.g. directly in wood preservative production e.g. as a working solution, which means that no waste solution or waste water is produced at all.
• arsenic can be recovered from the solution and recir- culated into a wood preservative production process, so that the waste water is substantially clean. Furthermore, residual arsenic is effectively separated from the washed combustion gases.
• the invention discloses a significant alter- native for the utilization of wood treated with a wood preservative, making it possible to reduce the amount of waste wood transported to dumping places, thus reducing the risk of heavy metals dissolved from the wood getting into the ground and ground water.
• a fur- ther advantage is a reduction in the amount of waste wood that may be classified as problem waste, which reduces the waste treatment costs.
• the method of the invention is effective and it can be easily implemented in conjunction with existing equipment. The method is also economical in respect of operating costs .
• Fig. 1 presents a block diagram representing the method of the invention
• Fig. 2 and 3 present block diagrams representing methods according to the invention for the treatment of condensation water and/or wash water.
• Fig. 1 presents a block diagram representing the treatment of wood impregnated with a wood preservative and the recovery of detrimental substances.
• the impregnated waste wood was chipped, producing 96 solid m 3 of wood chips.
• the wood material contained heavy metals as follows: Cu 0,74 kg/solid m 3 As 1,04 kg/solid m 3 Cr 1,03 kg/solid m 3
• the wood chips were burned in the boiler.
• the amount of ashes produced as a result of the combustion was about 1000 kg, which contained 66 kg of copper, 30 kg of arsenic and 99 kg of chromium.
• the ashes were fed into a copper smelter, where they were processed together with concentrates.
• Most of the copper was recovered as metallic copper via copper electrolysis.
• the chromium and part of the arsenic was bound in slag.
• Most of the arsenic was recovered in the form of Cu 3 As precipitate in conjunction with the copper electrolysis.
• the precipitate was utilized by a method disclosed in specification US 5141753. By this method, a CCA concentrate needed in wood preservative manufacture is produced from Cu 3 As precipitate .
• the combustion gases produced in the combus- tion process were cooled down to 200 - 300 °C and washed in a high-pressure Venturi washer, where most of the arsenic was absorbed in water.
• the arsenic acid produced as a result of oxidation and the wash/condensation water formed a weak arsenic acid solution, which could be used directly as a weak working solution in the production of wood preservative, by adding to it some copper chromate, which was obtained by mixing CuO and Cr0 3 together.
• the composition of the working solution obtained was CuO 2.81 g/dm 3 , Cr0 3 6.76 g/dm 3 and As 2 0 5 4.85 g/dm 3 .
• the solution was suited for use in class A impregnation in accordance with NTR norms . Based on the experiment, it was possible to recover the arsenic from the combustion gases with a good yield and in an environmentally friendly manner. Measurements pertaining to industrial hygiene performed in the hall indicated that the workers were not exposed to heavy metals during the experiment.
• the flow of combustion gases produced by the combustion of wood treated with a wood preservative was 5000 Nm 3 /h and its temperature was 1100 °C .
• the combustion gas contained 5648 kg of dry gas/m 3 .
• the water content of the gas was 153 g/kg of dry gas and the As content 230 mg/kg of dry gas.
• the combustion gas was cooled down to 250 °C via indirect cooling and passed into a Venturi washer, where it was cooled further to a temperature of 50 °C .
• the gas was purified in the Venturi washer and the washed gas was heated again to a temperature of about 64 °C via indirect heating.
• the water content of the gas was 90 g/kg of dry gas and the As 2 0 3 content 3 mg/kg of dry gas.
• the gas was passed into a fabric filter, in which residual heavy metals were removed from the gas (Fig. 1) . After the filtering, the As 2 0 3 content of the gas was 0.04 mg/kg of dry gas. The dust emissions and the amount of PAH compounds in the gas were also low.
• the combustion of CCA- impregnated wood produced 10 dm 3 of condensation/wash water.
• the condensation water contained As 2 0 3 3.29 g/dm 3 , As 2 0 5 0.26 g/dm 3 , Cu 2+ 1 mg/dm 3 and Cr 3+ 0.5 mg/dm 3 .
• the solution was oxidized as in Example 1.
• Fig. 2 presents a block diagram representing a method for the treatment of condensation/wash water.
• the arseniferous condensation water, 10 dm 3 which had an As 2 0 3 content of 3.55 g/dm 3 and an As 2 0 5 content of 0.5 g/dm 3 , was oxidized at a temperature of 98 °C using oxygen, producing arsenic acid.
• the solution was passed through a 1 dm 3 reactor, in which it was intensively agitated.
• the reactor had been filled with 2 kg of chopped copper wire mate- rial.
• 50 % hydrogen peroxide was supplied into the reactor at 8 ml/h.
• the arsenic was precipitated according to reaction (III) .
• the temperature during the reaction was 55 °C.
• the copper arsenic precipitate produced was removed from the upper part of the reactor, leaving the copper wire material in the reactor. After the precipitation, the pH of the solution was 3.5. By adding a small amount of NaOH, the pH value of the solution was increased to 5.5. The arsenic content of the solution was 30 mg/dm 3 and its copper content was 40 mg/dm 3 .
• the final solution was purified in the manner described in Example 4 and Fig. 2, i.e. the residual arsenic was precipitated. The copper arsenic precipitate was separated by filtering.
• the precipitate was mixed with Cr0 3 and H 3 As0 4 , thus obtaining a strong CCA concentrate in which the amount of active material was 800 g/dm 3 and which contained 13.7 % CuO, 34.2 % Cr0 3 and 24.1 % As 2 O s and 28 % H 2 0.
• Fig. 3 presents a block diagram representing a method for the treatment of condensation/wash water.
• Condensation/wash water oxidized as in Example 1 was supplied into a 3 dm 3 reactor which contained 2 kg of Cu 3 As precipitate.
• Cu 3 As precipitate is a waste material which is produced as a side product in copper industry (Fig. 1) .
• the same charge of Cu 3 As precipitate could be used to treat a plurality of repeated single condensation/wash water charges, e.g. 50 - 100 charges, because the reaction took place quickly and there was a stoichiometric excess of Cu 3 As precipitate in relation to arsenic acid.
• Different embodiments of the method of the invention are applicable for the combustion of various kinds of waste wood and/or for the recirculation, recovery and/or utilization of heavy metals, especially arsenic and copper.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Organic Chemistry (AREA)
• Environmental & Geological Engineering (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Materials Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Analytical Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Geology (AREA)
• Biomedical Technology (AREA)
• Health & Medical Sciences (AREA)
• Water Supply & Treatment (AREA)
• Hydrology & Water Resources (AREA)
• Processing Of Solid Wastes (AREA)
• Treating Waste Gases (AREA)

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Citations (4)

• 1999
  • 1999-04-30 FI FI990984A patent/FI107788B/sv active
• 2000
  • 2000-04-26 AU AU41239/00A patent/AU4123900A/en not_active Abandoned
  • 2000-04-26 EP EP00920787A patent/EP1198305A1/en not_active Withdrawn
  • 2000-04-26 WO PCT/FI2000/000360 patent/WO2000066286A1/en active Search and Examination

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