METHOD AND SYSTEM FOR ASH TREATMENT

Abstract

A method of the invention for treatment of particulate material for metal recovery includes heating a furnace to a first temperature, feeding a particulate material into the furnace, and before or after heating of the raw material, feeding a reducing gas flow through the furnace. The particulate material is heated in the furnace for volatilizing one or more metals contained in the ash into the gas flow, and the volatilized particles are recovered in one or more collection units. A system for treatment of particulate material for metal recovery includes a heated furnace for receiving flows of reduction gas and particulate material, a collection unit for volatilized particles, and a collection unit for non-volatilized material.

Claims

1.-21. (canceled)

22. A method for treatment of combustion ash for metal recovery, the method comprising the steps of: a) heating a continuous flow-through furnace to a first temperature, b) feeding a combustion ash into the continuous flow-through furnace, c) feeding oxidizing gas through the continuous flow-through furnace, d) heating the combustion ash fed into the continuous flow-through furnace in the first temperature for volatilizing chlorides contained in the ash, and removing the chlorides, e) changing the conditions in the continuous flow-through furnace by feeding a reducing gas flow through the continuous flow-through furnace, f) changing the temperature of the continuous flow-through furnace to a second temperature for heating the combustion ash in the furnace for volatilizing one or more metals contained in the ash into the gas flow, and g) recovering the vaporized particles in one or more collection units.

23. The method of claim 22, wherein the combustion ash is selected from one of bottom ash or fly ash, fly ash containing one or more of Si, Ca, Al, Zn, Na, Sb, Bi, K, Fe, Co, Cu, Ni, and/V and bottom ash containing Si, Al, Zn, Sb, Bi, Fe, Co, Cu, Ni, and/V.

24. The method of claim 22, wherein the combustion ash is bottom ash and the first temperature is sufficient for volatilizing Zn, Bi, and/or Sb, preferably about 1000° C.

25. The method of claim 22, wherein in step f), the resting volatilizing metals in the combustion ash, such as Cu, are volatilized in gaseous form into the gas flow, and thereafter performing step g) also for Cu.

26. The method of claim 22, wherein the reduction gas in step e) is a mixture of nitrogen and hydrogen gases and/or carbon monoxide, CO, gas.

27. The method of claim 22, wherein the gas flow with the volatilized gases are quenched before the recovering step g).

28. The method of claim 27, wherein the quenching is performed with a quenching gas before the gas flow with the volatilized metals are cooled down in such conditions and with such a speed that aerosol particles of nanosize are formed.

29. The method of claim 22, wherein the combustion ash comprises fly ash, and further comprising chlorides of one or more of Na, K, Ca, and/or Cd.

30. The method of claim 29, wherein the first temperature for volatilizing chlorides is 800-900° C. and the second temperature for volatilizing metals in step f) is sufficient for volatilizing Zn, Bi and Sb, preferably about 1000° C.

31. The method of claim 29, wherein the oxidizing gas for volatilizing chlorides of one or more of Na, K, Cu, Pb, is a gas flow of air fed into the furnace.

32. The method of claim 29, wherein the chlorides are removed after volatilizing and quenching by collecting with filter bags.

33. The method of claim 29, wherein the heating of the combustion ash is continued after step f) in the furnace by raising the temperature into a third temperature, whereby resting volatilizing metals in the combustion ash, such as Cu, are volatilized in gaseous form into the gas flow, and thereafter performing step g) for Cu and said other vaporized gases.

34. The method of claim 22, wherein Cd is volatilized and removed before step a) by feeding a reducing gas through the furnace heated into a preliminary temperature for volatilizing Cd, and preferably in a temperature around 500° C.

35. The method of claim 29, wherein the chloride removal is performed in one rotary kiln furnace and the combustion ash is after chloride removal fed to another rotary kiln furnace for performing step f).

36. The method of claim 29, wherein step f) is performed in the same rotary kiln reactor as the chloride removal.

37. The method of claim 22, wherein the metals are recovered by collecting with a filter.

38. The method of claim 22, wherein compounds not volatilized in step f) are residuals and they are separated, heated, and pulverized.

39. The method of claim 38, wherein the non-vaporized compounds are Si, Ca, Al, Fe, Co, Mg, Ni, P, Ti, As, and V and non-volatile forms of Na and K.

40. A system for treatment of combustion ash for metal recovery, the system comprising: a) a heated continuous flow-through furnace for receiving flows of reduction gas and combustion ash, b) a first collection unit for volatilized particles, and c) a second collection unit for non-volatilized material.

41. The system of claim 40, further comprising a cooling unit for quenching aerosol particles formed from the combustion ash.

42. The system of claim 40, wherein the furnace is a rotary kiln reactor.

Description

FIGURES

[0076] FIG. 1 is a schematic view of a first embodiment of the system of the invention for recovering metals from fly ash in a one-phase rotary kiln furnace

[0077] FIG. 2 is a schematic view of a second embodiment of the system and method of the invention for recovering metals from fly ash in a two-phase rotary kiln furnace

[0078] FIG. 3 is a schematic view of a third embodiment of the system and method of the invention for recovering metals from bottom ash in a rotary kiln furnace

[0079] FIG. 4 is a schematic view of a fourth embodiment of the system and method of the invention for recovering metals from fly ash in an induction furnace

DETAILED DESCRIPTION

[0080] FIG. 1 is a schematic view of a first embodiment of the system and method of the invention, wherein a one phase rotary kiln furnace is used for recovering metals from fly ash. The embodiment of FIG. 1 comprises the following steps and units.

[0081] Unit 1 is a container for combustion ash, fly ash in this embodiment, from which it is fed into a continuous rotary kiln furnace referred to with reference number 4.

[0082] Unit 2 is a container for oxidizing gas, such as air, which is fed into and through the furnace 4.

[0083] Unit 3 is a container for reduction gas, such as a hydrogen gas/nitrogen gas (H.sub.2/N.sub.2) mixture, which also is fed into the furnace 4 and through that.

[0084] If the fly ash contains Cd it is volatilized in a preliminary step by feeding reducing gas, such as a H.sub.2/N.sub.2 mixture, from unit 3 into the furnace 4 and by heating the furnace 4 to a preliminary temperature of ca 500° C. The volatilized Cd is quenched in a cooling unit (not shown) with e.g. nitrogen or possibly with air and collected in a collection unit (not shown), which can consist of one or more filter bags.

[0085] The furnace 4 is then heated into a first temperature of approximately 850° C. for volatilizing (other) existing chlorides contained in the fly ash in oxidation gas, such as air. The chlorides, which mostly are in the form of NaCl and KCl, are volatilized as such. There can also be CdCl.sub.2, which is volatilized. If the ash contains CaCl.sub.2), the chloride is freed from CaCl.sub.2) as HCl, and the Ca remains in the ash converted into CaO. There can also be chlorides of Pb and/or Cu, which also are collected as such.

[0086] The gas flow of volatilized chlorides of Na and/or K is then fed into a cooling unit 5, where they are quenched with air so that they can be collected in unit 6, unit 5 and 6 being separate from those used for quenching and collecting CdCl.sub.2.

[0087] Volatilized NaCl and/or KCl are collected in a collecting unit referred to with reference number 6, which can consist of one or more filter bags. Minor amounts of lead (II) chloride (PbCl.sub.2) and copper(II) chloride (CuCl) might also be found in the volatilizing chlorides. Even Cadmium chloride (CdCl.sub.2) can be found, if Cd has not been removed in a preliminary step referred to above. PbCl.sub.2 and CuCl can be precipitated (chrystallized) from NaCl and/or KCl products if their concentrations exceed acceptable ranges.

[0088] The gas flow now still contains hydrogen chloride (HCl), which is removed by a gas scrubber. Such a scrubber can generally be used to remove some particulates and/or gases from industrial exhaust streams. Traditionally, the term “scrubber” has referred to pollution control devices that use liquid to wash unwanted pollutants from a gas stream. Recently, the term has also been used to describe systems that inject a dry reagent or slurry into a dirty exhaust stream to “wash out” acidic gases.

[0089] The part of the volatilizing chlorides, which are in the form of HCl gas, is left in the reactor 4 to be removed in step 7 with a scrubber.

[0090] After removal of NaCl and KCl, the conditions in the furnace 4 are changed by feeding a reducing gas flow, e.g. a H.sub.2/N.sub.2 mixture, from gas container 3 to and through the furnace 4 and by stopping the flow of oxidation gas from container 2 to furnace 4.

[0091] The heating of the fly ash is continued in the furnace 4 by heating to a temperature of approximately 1000° C. for volatilizing Zn, Bi, and Sb in the atmosphere of said reducing gas.

[0092] Non-volatilized compounds of the ash are residuals that are collected in unit 8 e.g. for manufacturing end products like catalysts or water treatment chemicals.

[0093] The gas flow with the vaporized Zn, Bi, and/or Sb is then fed into a cooling unit 9 for quenching with nitrogen or possibly air with a speed with which the vaporized metals form nanosized aerosol particles. In this step, it is important with respect to the forming of particles of nanosize that the gas flow is not cooled down before mixing it with the diluting gas used for the quenching. The place for the dilution gas inlet as well as the speed, amount and temperature of the diluting gas flow therefore have to be chosen thereafter.

[0094] It is, however, not crucial for the metal recovery itself that the particles are of nanosize, but it is advantageous for preparing end products.

[0095] The nanosized aerosol Zn, Bi, and Sb particles are then recovered in a collection unit 10, which e.g. can be a filter bag.

[0096] The heating of the fly ash is continued in the furnace 4, which now is heated into a temperature of 1000-1400° C., whereby a further part of volatilizing metals, such as Cu, in the combustion ash are volatilized in gaseous form into the gas flow.

[0097] The gas flow with the volatilized Cu and other volatilizing metals is then fed into the same cooling unit 9 as for Zn, Bi and Sb for quenching with nitrogen or air and with a velocity with which these further part of volatilized metals form nanosized aerosol particles. Generally, the velocity, temperature, and place of the quenching and diluting gas is crucial so that particles of nanosized would be formed, since the gas flow should not cool down before the quenching.

[0098] The nanosized aerosol Cu and possible other metals are then recovered in a separate collection unit 11, which also ca be a filter bag.

[0099] FIG. 2 is a schematic view of a second embodiment of the system and method of the invention, wherein a two-phase process is used for recovering metals from fly ash. The embodiment of FIG. 2 comprises the following steps and units.

[0100] Unit 1 is a container for combustion ash, fly ash in this embodiment, from which it is fed into a continuous rotary kiln furnace referred to with reference number 3.

[0101] Unit 2 is a container for oxidizing gas, such as air, which is fed into and through the furnace 3.

[0102] If the fly ash contains Cd it can be volatilized in a preliminary step by feeding reducing gas, such as a H.sub.2/N.sub.2 mixture, from unit 9 into the furnace 3 and by heating the furnace 3 to a preliminary temperature of ca 500° C. The volatilized Cd is quenched in a cooling unit (not shown) with nitrogen or possibly with air and collected in a collection unit (not shown) by filter bags.

[0103] Furnace 3 is then heated into a temperature of approximately 850° C. for volatilizing existing chlorides contained in the fly ash in oxidation gas, such as air. The chlorides, which mostly are in the form of NaCl and KCl, are volatilized as such. There might also be minor amounts of CdCl.sub.2. If the ash contains CaCl.sub.2), the chloride is freed from CaCl.sub.2) as HCl, and the Ca remains in the ash converted into CaO.

[0104] The gas flow of volatilized chlorides is then fed into a cooling unit 5, where it is quenched with air so that they could be collected.

[0105] Volatilized NaCl and/or KCl are collected in a collecting unit referred to with reference number 6, which can consist of one or more filter bags. Minor amounts of PbCl.sub.2 and CuCl might also be found in the volatilizing chlorides. Even CdCl.sub.2 can be found, if Cd is not removed not removed in a preliminary step referred to above. PbCl.sub.2 and CuCl can be precipitated (chrystallized) from the mixture of chlorides if their concentrations exceed acceptable ranges.

[0106] The part of the volatilizing chlorides in the form of HCl gas is left in the reactor 3 to be removed in a later step with a scrubber (see reference number 7).

[0107] After removal of NaCl and KCl, non-volatilized compounds of the fly ash are collected in unit 4 for further treatment and recovery of metals.

[0108] This ash is fed to unit 8 and from there further to a rotary kiln furnace 10.

[0109] Unit 9 is a container for reducing gas, such as a H.sub.2/N.sub.2 mixture, which also is fed as a gas flow into the rotary kiln furnace 10.

[0110] The heating of the fly ash is continued in the furnace 10 by heating to a temperature of approximately 1000° C. for volatilizing Zn, Bi, and/or Sb in the atmosphere of said reducing gas.

[0111] The gas flow with the vaporized Zn, Bi, and/or Sb is then fed into a cooling unit 12 for quenching with nitrogen or possibly air with a speed and in conditions with which the vaporized Zn, Bi, and/or Sb form nanosized aerosol particles.

[0112] The nanosized aerosol Zn, Bi, and Sb particles are then recovered in a collection unit 13, which e.g. can be a filter bag.

[0113] The heating of the fly ash is continued in the furnace 10 by heating to a temperature of approximately 1000° C.-1400° C. for volatilizing a resting part of volatilizing metals, such as Cu in the atmosphere of said reducing gas. Cu is vaporized in gaseous form into the gas flow.

[0114] The gas flow with the vaporized Cu and other resting volatilizing metals is then fed into the same cooling unit 12 as for Zn, Bi and Sb for quenching with nitrogen or possibly air with a speed and in conditions with which this part of volatilized metals form nanosized aerosol particles.

[0115] The nanosized aerosol Cu and other possible metals are then recovered in a separate collection unit 14, which also can be a filter bag.

[0116] Non-volatilized compounds of the ash are residuals that are collected in unit 11 e.g. for manufacturing end products like catalysts or water treatment chemicals.

[0117] The gas flow now still contains HCl, which is removed by a gas scrubber 15. Such a scrubber can generally be used to remove some particulates and/or gases from industrial exhaust streams.

[0118] FIG. 3 is a schematic view of a third embodiment of the system and method of the invention for recovering metals from bottom ash in a rotary kiln furnace. The embodiment of FIG. 3 comprises the following steps and units.

[0119] Unit 1 is a container for combustion ash, bottom ash in this embodiment, from which it is fed into a continuous rotary kiln furnace referred to with reference number 4.

[0120] Unit 3 is a container for reduction gas, such as a H.sub.2/N.sub.2 mixture, which is fed into and through the furnace 4.

[0121] The heating of the bottom ash is continued in the furnace 4 by heating to a temperature of approximately 1000° C. for volatilizing Zn, Bi and/or Sb in the atmosphere of said reduction gas.

[0122] The gas flow with the volatilized Zn, Bi and/or Sb is then fed into a cooling unit 8 for quenching with nitrogen or possibly air with a speed and in conditions with which the volatilized metals form nanosized aerosol particles.

[0123] The nanosized aerosol Zn, Bi, and Sb particles are then recovered in a collection unit 9, which e.g. can be a filter bag.

[0124] The heating of the bottom ash is still continued in the furnace 4 by heating to a temperature of approximately 1000° C.-1400° C. for volatilizing also a further part of volatilizing metals, such as Cu, in the atmosphere of said reducing gas and Cu is vaporized in gaseous form into the gas flow.

[0125] Non-volatilized compounds of the ash are residuals that are collected in unit 7 e.g. for manufacturing end products like catalysts or water treatment chemicals.

[0126] The gas flow containing volatilized Cu and other volatilizing metals is then fed into the same cooling unit 8 as for Zn, Bi and Sb for quenching with nitrogen or possibly air in conditions in which and with a speed with which this further part of volatilized metals form nanosized aerosol particles.

[0127] The nanosized aerosol Cu and other metals are then recovered in a separate collection unit 10, which also ca be a filter bag.

[0128] Reference number 11 stands for preparing end products. End products from Cu and Zn might be needed in cosmetics, paints, electronics, and different nanomaterials.

[0129] FIG. 4 is a schematic view of a fourth embodiment of the system and method of the invention for recovering metals from fly ash in an induction furnace. The embodiment of FIG. 4 comprises the following steps and units.

[0130] Unit 1 is a container for combustion ash, fly ash in this embodiment, from which it is fed into an induction furnace referred to with reference number 4.

[0131] Unit 2 is a container for oxidizing gas, such as air, which is fed into and through the furnace 4.

[0132] Unit 3 is a container for reducing gas, such as a H.sub.2/N.sub.2 mixture, which also is fed into the furnace 4 and through that.

[0133] If the fly ash contains Cd, it is volatilized in a preliminary step by feeding reducing gas, such as a H.sub.2/N.sub.2 mixture, from unit 3 into the furnace 4 and by heating furnace 4 to a preliminary temperature of ca 500° C. The volatilized Cd is quenched in a cooling unit (not shown) with e.g. nitrogen or possibly with air and collected in a collection unit (not shown), which can consist of one or more filter bags.

[0134] The furnace 4 is then heated into a first temperature of approximately 850° C. for volatilizing (other) existing chlorides contained in the fly as in oxidation gas, such as air. The other chlorides, which mostly are in the form of NaCl and KCl, are volatilized as such. There might be minor amounts of CdCl.sub.2. If the ash contains CaCl.sub.2), the chloride is freed from CaCl.sub.2) as HCl, and the Ca remains in the ash converted into CaO. There can also be chlorides of Pb and/or Cu, which also are collected as such.

[0135] The gas flow of volatilized chlorides of Na and/or K is then fed into a cooling unit 5, where they are quenched with air so that they could be collected in unit 6, unit 5 and 6 being separate from those used for quenching and collecting CdCl.sub.2.

[0136] Volatilized NaCl and/or KCl are collected in a collecting unit referred to with reference number 6, which can consist of one or more filter bags. Minor amounts of PbCl.sub.2 and CuCl might also be found in the volatilizing chlorides. Even CdCl.sub.2 can be found, if not removed in a preliminary step referred to above. PbCl.sub.2 and CuCl can be precipitated (chrystallized) from NaCl and/or KCl products if their concentrations exceed acceptable ranges.

[0137] The part of the volatilizing chlorides, which are in the form of HCl gas, is left in the reactor 4 to be removed in step 7 with a scrubber. Such a scrubber can generally be used to remove some particulates and/or gases from industrial exhaust streams.

[0138] After removal of NaCl and KCl, the conditions in the furnace 4 are changed by feeding a reducing gas flow, e.g. a H.sub.2/N.sub.2 mixture, from gas container 3 to and through the furnace 4.

[0139] The heating of the fly ash is continued in the furnace 4 by heating to a temperature of approximately 1000° C. for volatilizing Zn, Bi, and Sb in the atmosphere of said reducing gas.

[0140] Non-volatilized compounds of the ash are residuals that are collected in unit 8 e.g. for manufacturing end products like catalysts or water treatment chemicals.

[0141] The vaporized metals form nanosized aerosol particles in the interaction with the gas flow. The nanosized aerosol Zn, Bi, and Sb particles are then recovered in a collection unit 9, which e.g. can be a filter bag.

[0142] The heating of the fly ash is continued in the furnace 4, which now is heated to a temperature of 1000-1400° C., whereby a further part of volatilizing metals, such as Cu, in the combustion ash are volatilized in gaseous form into the gas flow.

[0143] The nanosized aerosol Cu and possible other metals are then recovered in a separate collection unit 10, which also ca be a filter bag.

[0144] If an induction furnace is used for treatment of bottom ash, no chloride removal needs to be performed, whereby units 2, 5, 6, and 7 are not needed.

EXAMPLES

[0145] The following examples were performed to show generally the volatilities of the chlorides and metals to be covered from fly ash in the conditions of the invention.

Example 1 (Flow-Through Furnace

[0146] Fly ash samples (0.05-1.0 g) from a grate-fired municipal solid waste incineration (MSWI) plant, with the chemical composition presented in the table below and with a maximum particle size of 250 μm, were heated in an electrically-heated, laminar flow-through tube reactor at different temperatures spanning the range 200-1050° C.

[0147] The samples were heated first in an oxidizing gas atmosphere (air) (=case a)) and then in a reducing gas atmosphere (=case b)) consisting of 10% v/v H.sub.2 and 90% v/v N.sub.2.

[0148] A porous tube dilutor, connected to the outlet of the reactor tube and positioned inside the reactor, was used to quench and dilute the hot product gases (Lyyränen et al., 2004; Backman et al. 2002) vaporized as a consequence of the heating.

[0149] Samples of metal condensates, which formed during said product gas quenching, were collected on quartz filter elements.

[0150] Gaseous emissions were measured with a Fourier-Transform Infrared (FTIR) gas analyser to obtain the gas composition exiting the reactor.

[0151] The volatilities of the elemental constituents of the fly ash were quantified by mass balance based on chemical analysis of the heat-treated ashes.

TABLE-US-00001 TABLE Elemental composition of the municipal waste combustion plant fly ash concentration Element (dry basis) C 1.3 % w/w S 4.2 % w/w H <0.3 % w/w N <0.1 % w/w Cl 6.5 % w/w Na 3.7 % w/w K 3.1 % w/w P 0.9 % w/w Ca 16.5 % w/w Mg 1.4 % w/w Si 8.1 % w/w Al 4.0 % w/w Fe 1.3 % w/w Ti 1.5 % w/w Zn 1.6 % w/w Sb 749 mg/kg As 71 mg/kg Cd 129 mg/kg Cr 520 mg/kg Cu 707 mg/kg Pb 1346 mg/kg Mn 829 mg/kg Ni 100 mg/kg Sn 653 mg/kg Bi 26 mg/kg Co 39 mg/kg Mo 19 mg/kg V 30 mg/kg Ag 9 mg/kg Au <1 mg/kg Tl <1 mg/kg

Case a) Release of Elemental Constituents to the Gas Phase in Air

[0152] The release of chlorides calculated as chlorine commenced between 600 and 700° C. and was virtually complete (>99% released) by 900° C. The release of S commenced between 800 and 850° C. and increased to 41% with increasing temperature to 1050° C. Carbon was predominately released between 500 and 600° C. The release of C commenced below 400° C. and was more or less complete (>99% released) by 1000° C. The release of Na and K (as their chlorides) commenced between 600 and 700° C. At 900° C., around 55% of Na and 80% of K were released to the gas phase. Further heating of the fly ash above 900° C. did not result in additional release of Na and K.

[0153] Powder X-ray diffraction analysis of heat-treated ashes and thermodynamic equilibrium calculations indicated that residual Na was retained in the ashes in the form of non-volatile aluminosilicates. The release of Cd commenced between 700 and 750° C. and reached 95% by 1050° C. The release of Pb commenced between 650 and 720° C. and reached 94% by 1050° C. The release of Zn commenced around 850° C. Only a minor fraction of Zn (<15%) was released by 1050° C. Copper was released within the temperature range 700-900° C. Around 50% of Cu was released following heating at temperatures above 900° C. Bismuth was non-volatile below 1000° C. Only a minor fraction of Bi (15%) was released at 1050° C. The following elements showed negligible volatility in air below 1050° C.: P, Ca, Mg, Ti, Al, Sb, Sn, and As.

[0154] Thus, the metals to be recovered in the invention are not significantly vaporized in oxidizing conditions.

Case b) Release of Elemental Constituents to the Gas Phase in a Gaseous Mixture Consisting of 10% Hydrogen and 90% Nitrogen.

[0155] The release profiles for CI and K in 10% H.sub.2 were similar to their release profiles in air. The release of Na in 10% H.sub.2 was almost identical to that in the air gas atmosphere for temperatures below 900° C. Above this temperature, Na was released to a greater extent in 10% H.sub.2 than in air. The release of Na at 1050° C. in 10% H.sub.2 was 78% (c.f. 53% in air at 1050° C.). Sulphur was released to a greater extent in 10% H.sub.2 than in air. The release of S in 10% H.sub.2 commenced between 600 and 700° C. (at least 100° C. lower than the onset temperature for S release in air). The hydrogen gas atmosphere inhibited the complete release of carbon. Around 8% of C remained in the ashes following heat-treatment at 1050° C. (c.f.<1% retention of C in air at 1050° C.). The release of Cd commenced between 290 and 400° C., and reached around 80% by 460° C. and 90% by 700° C. The release of Zn was significant at temperatures above 600° C. and reached around 80% by 900° C. and around 87% by 1050° C. The release of Pb was greater in 10% H.sub.2 than in air over the temperature range 600-725° C. The extent of release of Pb was similar in 10% H.sub.2 to that in air for temperatures within the range 785-1050° C. Copper was significantly less volatile in 10% H.sub.2 than in air. The release of Cu was minor below 880° C. (<10% release). At 1050° C., around 25% of Cu was released to the gas phase. The release of Sb and Sn commenced between 600 and 700° C. and reached around 70-75% by 1000° C. Arsenic was released to only a minor extent (around 30% at 1050° C.). The onset of As release commenced around 700-800° C. The release of Bi commenced around 500-600° C. and reached around 85-90% by 880° C. The following elements showed negligible volatility in 10% H.sub.2 below 1050° C.: P, Ti, Ca, Mg, and Al.

Example 2 (Induction Furnace

[0156] The same fly ash sample used in Example 1 was heated in an induction furnace in a gas atmosphere consisting of H.sub.2 (10% v/v) and N.sub.2 (90% v/v). Samples of fly ash (10-14 g) were loaded into the induction furnace. The induction furnace was then sealed and heated to 1100° C. Material which volatilized from the fly ash at 1100° C. was quenched and then collected on a filter.

[0157] The collected condensate was composed of Zn (36.8%), K (19.0%), Na (11.5%), Pb (2.6%), Sn (0.9%) of the gravimetrically weighted mass. The resting 1.2% was composed of minor elements (Cr, Mn, Co, Ni, Cu, As, Mo, Ag, Cd, Sb, Ti, Bi) and unanalyzed, probably chlorine and sulphur, 28%.

[0158] The collected material was analysed for metal and metalloid concentrations by inductively-coupled plasma mass spectrometry (ICP-MS) following pressurized acid digestion. Treated ash residues were weighed and then analyzed for metals and metalloids by X-ray fluorescence (XRF) following sample digestion in a mixture of nitric acid and hydrochloric acid. The fractions of inorganic elements released to the gas phase were: CI 40.6%, S 69.5%, K 40.4%, Cu 0%, Ca 41.2%, P 81.1%, Pb 76.1% and for Zn 97.2%.

Thermal Fractionation of the Element Constituents of Fly Ash

[0159] Metal and metalloid contaminated MSWI fly ash can be heat-treated in two stages to achieve favourable fractionation of metals and metalloids. In the first stage, fly ash is heated at 900° C. in air to remove chlorides (>99% removal calculated as CI), C (>98% removal), and significant amounts of K, Na, Cd, Pb, and Cu from the ash removed in the form of chlorides.

[0160] The volatilized material can be quenched by hot gas dilution (Lyyränen et al., 2004, Backman et al. 2002) and then collected in an electrostatic precipitator (ESP) or bag filter. The collected material can potentially be utilized as road salt.

[0161] In the second stage of treatment, the hot (900° C.) reactor is purged of oxygen by flushing with nitrogen gas, and then hydrogen is fed into the reactor to create a gas atmosphere consisting of both hydrogen and nitrogen. The second stage of treatment causes Zn to volatilize and small amounts of valuable commodity elements, particularly Sn, Sb, and Bi, to volatilize. Antimony and bismuth are both classified as critical raw materials by the EU (http://ec.europa.eu/qrowthisectors/raw-materials/specific-interesticritical/).

[0162] Volatilized material is then quenched by hot gas dilution (Lyyränen et al., 2004) to form a zinc-rich condensate. The condensate can be collected in an ESP or bag filter. Gaseous zinc is transformed into zinc nanoparticles during hot gas dilution. The zinc nanoparticles can potentially be used to produce various high-value products (e.g. sunscreens, paints, electronics, solar cells, sensors etc.).

[0163] A similar procedure as for Zn can be performed later for Cu, especially for bottom ash, because there are no chlorides a relatively large amounts of Cu, but at a higher reactor temperature as Cu starts to vaporize at around 1100° C. and is completed at around 1350° C. according to chemical equilibrium.

REFERENCES

[0164] Lyyränen, J., Jokiniemi, J., Kauppinen, E. I., Backman, U., Vesala, H.

[0165] Comparison of Different Dilution Methods for Measuring Diesel Particle Emissions

[0166] (2004) Aerosol Science and Technology, 38 (1), pp. 12-23

[0167] Backman, U., Jokiniemi J. K., Auvinen, A., Lehtinen, K. E. J. (2002) The Effect of Boundary Conditions on Gas Phase Synthesised Silver Nanoparticles, Journal of Nanoparticle Research 4:325-335.