Process for producing iron chloride and aluminum chloride from sewage sludge incineration ash

Abstract

i) A step of reacting sewage sludge incineration ash containing at least one iron compound and an aluminum compound with at least one alkali metal chloride and / or at least one alkaline earth metal chloride at a temperature of 200°C to 1100°C in an inert gas atmosphere, and ii) Step of extracting and isolating the iron chloride and aluminum chloride formed in the exhaust gas stream. A process for producing iron chloride and aluminum chloride, characterized by including the following:

Description

Technical Field

[0001] The present invention relates to a process for producing iron chloride and aluminum chloride from iron compounds and aluminum compounds present in sewage sludge incineration ash.

Background Art

[0002] Iron chlorides such as Fe(II)Cl2 and Fe(III)Cl3 are typically produced from metallic iron. The same is true for aluminum, which is similarly produced from elemental aluminum. However, iron- or aluminum-containing compounds such as sewage sludge incineration ash, which have not been considered as alternative raw materials for producing the corresponding chlorides until now, are becoming increasingly available in large quantities.

[0003] In some waste materials containing iron-containing compounds, iron is an interfering element in reusing the main components of these waste streams. These include particularly sewage sludge incineration ash, which generally contains various iron compounds in a proportion ranging from the latter half of the single digits to the middle of the double digits (based on elemental iron). Iron compounds generally have very low solubility in water, and therefore, direct utilization lacks economic viability. Thus, for example, iron phosphate present in sewage sludge incineration ash has very low solubility even in a relatively high-concentration phosphoric acid solution. As a result, for example, it is not economical to use a phosphoric acid fertilizer highly contaminated with iron ions.

[0004] Thus, sewage sludge can be used as an additional source for producing iron chloride and aluminum chloride.

[0005] The reaction between phosphate and chlorides of alkali metals and / or alkaline earth metals has been repeatedly studied regarding the use of sewage sludge incineration ash. For directly using the ash in the agricultural industry, various alkali metal or alkaline earth metal chlorides have been mixed with sewage sludge for the purpose of reducing the required heavy metals, and heating has been carried out in air in a dry state.

[0006] Therefore, (Non-Patent Document 1) reports a dry reaction of sewage sludge incineration ash and magnesium chloride at temperatures below 1000°C in air, and as shown in Figure 5, it is found that the iron and aluminum components are substantially completely retained in the residue, and therefore, the aluminum and iron are not reduced.

[0007] Non-patent document 2 similarly reports that a test was conducted to remove Cd, Cr, Cu, Ni, Pb, and Zn from sewage sludge incineration ash by adding KCl or MgCl2 at a temperature exceeding 900°C in air, and no reduction in iron or aluminum was observed. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] Christian Adam et al.,(Materials Transactions,Vol.48,No.12(2007)pp.3056-3061) [Non-Patent Document 2] Mattenberger et al.,Waste Management 28(2008)2709-2722 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Therefore, the present invention aims to provide a suitable process that uses iron compounds and aluminum compounds present in sewage sludge incineration ash as starting materials. [Means for solving the problem]

[0010] Surprisingly, i) A step of reacting sewage sludge incineration ash containing at least one iron compound and an aluminum compound with at least one alkali metal chloride and / or at least one alkaline earth metal chloride in an inert gas atmosphere containing oxygen at a temperature of 200°C to 1100°C, preferably less than 200 ppm, and ii) Step of extracting and isolating the iron chloride and aluminum chloride formed in the exhaust gas stream. A process for producing iron chloride and aluminum chloride, characterized by including [a specific compound], is found herein. [Modes for carrying out the invention]

[0011] Sewage sludge incineration ash Sewage sludge incineration ash should preferably be understood to mean the solid residue produced in both sewage sludge combustion and sewage sludge gasification for the production of fuel gas. Sewage sludge preferably contains iron phosphate such as aluminum phosphate and calcium iron phosphate (e.g., Ca9Fe(PO4)7 or phytrocite Ca3(PO4)2), gypsum, calcium hydroxide, oxides and carbonates, iron oxides such as hematite (Fe2O3), and quartz (SiO2), indialite (Mg2Al4Si5O 18 It may contain various components such as ), and these are just a few examples.

[0012] The sewage sludge incineration ash preferably contains iron compounds (calculated as elemental iron) in a proportion of 1% to 21% by weight, and aluminum compounds in a proportion of 0.7% to 20.2% by weight in terms of elemental aluminum.

[0013] The total amount of iron and aluminum compounds is preferably 1.7% to 41.2% by weight in terms of each elemental metal. A preferred composition of the sewage sludge incineration ash is that it contains at least one phosphate source in an amount of at least 1% by weight based on the sewage sludge incineration ash.

[0014] Sewage sludge incineration ash typically contains, preferably, the following additional elements in terms of their respective elemental equivalents. 4 wt% to 38 wt% calcium, 0 wt% to 2 wt% potassium, 0.1 wt% to 4 wt% magnesium, 0.1 wt% to 4 wt% sodium, 4 wt% to 40 wt% phosphate PO4 3- , 0 wt% to 7 wt% sulfur, 0 wt% to 24 wt% silicon, and 0 wt% to 2 wt% titanium.

[0015] These elements together preferably constitute more than 70 wt% of the sewage sludge incineration ash in terms of oxide conversion.

[0016] Each constituent component may preferably exist in the form of an oxide or a phosphate or a sulfate. The iron compound preferably exists as an iron (III) compound at about 50 to 100 wt%. It is preferable that 80 wt% or more of the phosphate exists as a metal phosphate of aluminum, calcium or iron.

[0017] The sewage sludge incineration ash further contains a number of additional elements in trace amounts, including particularly copper, zinc, lead, barium and manganese. The aforementioned silicon is substantially in the form of sand and mainly comes from the filtration process commonly performed at sewage treatment plants.

[0018] Alkali metal chlorides Suitable alkali metal chlorides preferably include NaCl, KCl, LiCl and mixtures thereof. NaCl or KCl, or a mixture of NaCl and KCl is preferred. When NaCl is used in a mixture with other alkali metal chlorides, particularly KCl, the mixing weight ratio is preferably 10:1 to 0.1:1, particularly 5:1 to 0.5:1.

[0019] The alkali metal chloride is preferably employed in an amount of 1 to 5 mol per 1 mol of the total number of moles of iron and aluminum present in each case, for example, measured by elemental analysis.

[0020] For measurements such as elemental analysis carried out by, for example, ICP-OES or ICP-MS, in each case, per mole of the total number of moles of iron and aluminum present in the mixture, it is preferable to employ an alkali metal chloride in an amount of 5:1 to 1:1 (mol / mol).

[0021] Alkaline earth metal chloride Suitable alkaline earth metal chlorides include, in particular, MgCl2, CaCl2 or mixtures thereof. MgCl2 is preferred.

[0022] A mixture of an alkaline earth metal chloride and an alkali metal chloride in a weight ratio of 4:1 to 0.25:1, particularly 2:1 to 0.5:1, especially a mixture of MgCl2 and NaCl and / or KCl, is preferred. It is particularly preferred to employ a mixture of KCl, NaCl and MgCl2.

[0023] Similarly, it is preferred to employ a mixture of MgCl2 and KCl in a weight ratio of 3:1 to 0.5:1.

[0024] Others Preferably, the process is characterized in that, in terms of metal, the molar ratio of chlorine from the employed alkali metal chloride and alkaline earth metal chloride to the total of iron and aluminum present in the mixture, preferably measured by elemental analysis, carried out by, for example, ICP-OES or ICP-MS, is 1 to 6.

[0025] Optionally, prior to the thermal reaction step, preferably as a mixture of suitable alkali metal and / or alkaline earth metal chlorides, sewage sludge incineration ash is briquetted, pelletized or extruded, and optionally, thereafter, heat pretreatment is carried out at 100°C to 199°C. Auxiliary agents such as phyllosilicates such as bentonite, lignosulfonates, methylcellulose, water glass, starch, etc. can be used for this purpose.

[0026] Process The input materials to be used, such as sewage sludge incineration ash and alkali metal chlorides and / or alkaline earth metal chlorides, are preferably mixed in a dry form in the mixer. Preferably, the mixer used is a paddle mixer or mill, such as a ball mill. The latter has the advantage that good homogenization of the reactants used can also be achieved by fine grinding. Preferably, this is followed by briquetting, pelletizing, or extrusion molding.

[0027] To protect any hygroscopic components present from water absorption, which could adversely affect the process yield, it is advantageous to perform even the step of mixing the reactants in an inert gas atmosphere, preferably in the absence of water.

[0028] The reaction itself is preferably carried out in the absence of air and water. Preferred inert gases include nitrogen, argon, or carbon dioxide. The inert gas atmosphere preferably contains less than 200 ppm of oxygen, and more preferably less than 100 ppm.

[0029] The reaction of sewage sludge incineration ash containing iron and aluminum compounds may be carried out in a fluidized bed, dumped bed, or moving bed reactor, in a shaft furnace, or preferably in an atmosphere furnace (in its simplest form, it can be considered as an indirectly heated tubular or rotary furnace). The products formed by the reaction, which are volatile at the reaction temperature (here in particular not only iron chloride, but also aluminum chloride, and optionally further heavy metal chlorides), are preferably resublimated and recovered together in a cold spot at a temperature below 150°C, or resublimated and recovered separately in different cold spots.

[0030] In a preferred embodiment, the formed iron chloride is isolated from the exhaust gas stream by resublimation, and the aluminum chloride is isolated from the exhaust gas stream by resublimation.

[0031] The preferred precipitation temperature for FeCl2 is less than 700°C, particularly between 700°C and 307°C; for FeCl3, it is less than 307°C, particularly between 150°C and 300°C; and for AlCl3, it is less than 150°C, particularly between 110°C and 149°C.

[0032] The iron recovered in the form of iron(III) chloride and / or iron(II) chloride according to the present invention is already of very high purity and can then be converted to a desired raw material form of iron. Examples include a wide variety of different forms of iron sulfate, iron nitrate, iron phosphate, or iron oxide.

[0033] Alternatively, iron chloride can be directly introduced as a gaseous stream into an aqueous medium containing sulfuric acid, nitric acid, or phosphoric acid, even without precipitation by resublimation, thereby forming the corresponding iron(III) sulfate, iron(III) nitrate, or iron(III) phosphate. Iron(II) sulfate, iron(II) nitrate, or iron(II) phosphate can also be obtained by using a suitable reducing agent in combination during the reaction.

[0034] However, it is preferable to separate iron chloride from the exhaust gas flow by resublimation.

[0035] Alternatively, aluminum chloride can be directly introduced as a gaseous stream into an aqueous medium containing sulfuric acid, nitric acid, or phosphoric acid, without being precipitated by resublimation, thereby forming the corresponding aluminum sulfate, aluminum nitrate, or aluminum phosphate.

[0036] However, it is preferable to separate aluminum chloride from the exhaust gas flow by resublimation.

[0037] The residue after the reaction preferably contains phosphates of the alkali and / or alkaline earth metal groups used, and optionally further phosphates, such as Ca3(PO4)2.

[0038] The resulting residue is preferably treated by adding 0.1 to 5 moles of phosphoric acid per mole of phosphate, preferably 0.2 to 1 mole of phosphoric acid per mole of phosphate. The reaction residue can therefore be directly converted into a water-soluble salt form suitable for agricultural use.

[0039] temperature The reaction is preferably carried out at a temperature of 400°C to 1000°C. The reaction typically takes 5 minutes to 10 hours, preferably 2 to 5 hours.

[0040] Use of residue While natural iron phosphate is particularly found in iron ore deposits such as pyrrhotite deposits, sewage sludge incineration ash containing iron phosphate compounds is produced, for example, during the incineration of sewage sludge, and this contains phosphates in a high proportion (up to 40% by weight).

[0041] Sewage sludge incineration ash is generally in the form of a mixture of different phosphates, such as calcium phosphate, iron phosphate, and aluminum phosphate. The exact composition / metal cation ratio depends on the phosphate precipitation technology used by the sewage treatment plant where the sludge is generated. Iron phosphate, which is very often produced during the precipitation process in sewage treatment plants, is one of the most common phosphates.

[0042] One method for making phosphates present in sewage sludge incineration ash usable by plants is digestion with HCl or H2SO4, as described, for example, in European Patent No. 3 623 348 B1. This process employs a solution, and therefore suffers from poor space-time yield. Numerous chemicals, such as various alkalis, acids, and limewater, are employed, thus complicating the process and increasing its cost. Filtration steps, such as those for iron hydroxide and aluminum hydroxide, are technically complex and therefore costly. At the same time, the chlorides used, derived from HCl, cannot be extracted as a product, resulting in the formation of large amounts of waste.

[0043] The thermal process is also described, for example, in Christian Adam et al. (Materials Transactions, vol.48, no.12 (2007) pp.3056-3061).

[0044] Therefore, the present invention also relates to a process for producing water-soluble phosphate compounds having a water solubility of more than 1 g / l at 20°C. i) A step of reacting sewage sludge incineration ash containing at least one iron compound and an aluminum compound with at least one alkali metal chloride and / or at least one alkaline earth metal chloride in an inert gas atmosphere containing oxygen at a temperature of 200°C to 1100°C, preferably less than 200 ppm. ii) A step of removing the iron chloride and aluminum chloride formed in the exhaust gas flow, iii) The obtained residue is treated by adding 0.1 to 5 moles of mineral acid per mole of phosphate in the residue, preferably 0.2 to 1 mole of mineral acid per mole of phosphate in the residue, to obtain a water-soluble phosphate compound. It is characterized by including.

[0045] Suitable mineral acids in step iii) include, for example, sulfuric acid, hydrochloric acid, nitric acid and / or phosphoric acid, where phosphoric acid is preferably used.

[0046] The reaction residue can therefore be converted in step iii) into a water-soluble salt and / or a citric acid-soluble salt, which are suitable for agricultural use as is.

[0047] The preferred scope of this process also applies to the above.

[0048] reactor The materials used in the process according to the present invention are preferably introduced into a reactor provided with a layer that is resistant under the set reaction conditions. Preferred reactor materials are nickel-coated or graphite-coated reactors. The reactor used may be a rotary tubular reactor or a tubular reactor, such as another type of reactor. Reactors that allow the materials to move around during the reaction are particularly preferred in order to make contact and heat distribution between reactants as effective as possible. Reactions in fluidized bed apparatuses and rotary tubular reactors or screw-type extruders are preferred.

[0049] In the case of a tubular reactor, the length of the reactor is preferably 0.2 to 40 m. The residence time in the reactor during the reaction is generally a function of temperature and the probability of contact between the reactants. The residence time in the reactor can be extended, for example, from 1 minute to 5 hours. The process according to the present invention can be carried out in batches or continuously. [Examples]

[0050] analysis After dissolving the sewage sludge incineration ash sample in a suitable acid, the sample was calibrated for specific elements using calibration standard solutions for each element, and then analyzed by ICP-OES.

[0051] X-ray diffractograms (XRDs) were recorded on the powder (flatbed) at a wavelength of 0.154 nm and a 2θ angle from 0° to 60°.

[0052] Example 1: 6.8g of sewage sludge incineration ash (according to XRD, it contains an iron-phosphorus compound including Ca9Fe(PO4)7, with composition (weight percent): Fe 13%, Al 1.5%, Ca 6.8%, Mg 0.44%, PO4) 3-A mixture containing 21% iron chloride and 0.52% Na was mixed with 1.4 g of KCl, 3.6 g of MgCl2, and 1.6 g of NaCl. The mixture was then first heated to 450°C in a crucible open to an anhydrous atmosphere and held at this temperature for 4 hours, then heated to 1000°C and held for another 4 hours. A weight loss of 21% was observed due to the sublimation of iron chloride and aluminum chloride.

[0053] To make the residue usable, the reaction time was extended, resulting in an iron-free residue that can be used for agricultural purposes.

[0054] The resulting residue exhibits characteristic reflections at 2θ 32.3° and 2θ 33.2° (wavelength: 1.54060 Å) in the X-ray diffractogram.

[0055] The resulting residue is mixed with 1.4 g of phosphoric acid to convert the formed magnesium phosphate and the present calcium phosphate into water-soluble forms. The powder is then granulated to have a total iron and aluminum content of less than 1% by weight on an elemental basis.

[0056] Example 2: 69g of sewage sludge incineration ash (according to XRD, it contains Ca9Fe(PO4)7 in particular, with a composition (weight percent) of Fe 13%, Al 1.5%, Ca 6.8%, Mg 0.44%, PO4 3- A mixture containing 21% sodium and 0.52% Na is subjected to a dense dry mixing with 14 g of NaCl and 17 g of MgCl2 (anhydrous). 56.2 g of the red mixture is placed in a quartz tube and immediately purged with dry nitrogen to prevent absorption of moisture from the air. The quartz tube is placed in a tubular furnace. During heating, a motor rotates the quartz tube in an oscillating motion at approximately 200° / min around its axis, thus continuously moving the powder bed. Simultaneously, a gas stream of purified nitrogen (oxygen <200 ppm v / v) at 0.5 l / min is passed through the tube, allowing it to pass over the sample. The tube outlet (=gas outlet) is narrowed with loosely inserted pieces of quartz wool.

[0057] The furnace and the sample in the quartz tube were heated to 1000°C (20K / min) while maintaining gas flow and oscillating rotational motion. After 120 minutes, the test was terminated, and the furnace and sample were cooled to room temperature under further nitrogen flow. The originally red powder turned white (47.2g), while a yellowish precipitate formed in the region above 200°C at the reactor outlet, and a white sublimation formed in the lower temperature region of approximately 100°C further away from the furnace. Verification by gas-phase infrared spectroscopy revealed the formation of a gas composed at least partially of HCl.

[0058] The white residue remaining in the tube (yield 47.2 g or 84%) was analyzed. Based on the mixture used, only 41% Fe, 64% Al, 61% Mg, and 72% Na were recovered.

[0059] To make the residue usable, the reaction time was extended, resulting in an iron-free and aluminum-free residue that can be used for agricultural purposes.

[0060] The amounts of phosphorus and calcium in the sample do not change during the reaction. The resulting residue shows characteristic reflections at 2θ 32.3° and 2θ 33.2° (wavelength: 1.54060 Å) in the X-ray diffractogram.

[0061] The resulting residue is mixed with 50 g of 85% phosphoric acid to convert the formed magnesium phosphate and the present calcium phosphate into water-soluble forms. The mixture thus obtained can optionally be granulated and used as a plant fertilizer.

[0062] The resulting white resublimation is aluminum chloride, and the yellowish resublimation is iron chloride; both can be recovered separately and are of high purity.

[0063] Example 3: 6.8g of sewage sludge incineration ash (according to XRD, it contains Ca9Fe(PO4)7 in particular, with a composition (weight percent): Fe 13%, Al 1.5%, Ca 6.8%, Mg 0.44%, PO4 3-Mix the 21% sodium (containing 0.52% Na) with 1.8 g of MgCl2 and 3.2 g of KCl. Place the red mixture into a quartz tube and immediately purge it with dry nitrogen to prevent absorption of moisture from the air. Place the quartz tube in a tubular furnace and purge it properly with purified nitrogen (0.5 l / min, oxygen <200 ppm v / v) for 30 minutes. Maintain a gas flow of 0.5 l / min of purified nitrogen (oxygen <200 ppm v / v) through the pipe and sample during the experiment and while the furnace heater is raising the temperature. The empty pipe outlet (=gas outlet) protruding from the oven is a furnace maintained at 100°C, and the mixture in the glass tube is heated to 750°C in the furnace.

[0064] The originally red powder turned white, while a yellowish precipitate formed in the region above 200°C at the reactor outlet, and a white sublimation formed in the lower temperature region of approximately 100°C further away from the furnace. The resulting white sublimation was aluminum chloride, and the yellowish sublimation was iron chloride; both can be recovered separately and are of high purity.

[0065] The amounts of phosphorus and calcium in the sample do not change as a result of the reaction.

[0066] The resulting residue is mixed with 50 g of 85% phosphoric acid to convert the formed magnesium phosphate and the present calcium phosphate into water-soluble forms. The mixture thus obtained can optionally be granulated and used as a plant fertilizer.

[0067] Similarly, the resulting sublimes can be reused for phosphate precipitation in wastewater treatment plants after purification to optionally remove unwanted heavy metals.

Claims

1. i) A step of reacting sewage sludge incineration ash containing at least one iron compound and an aluminum compound with at least one alkali metal chloride and / or at least one alkaline earth metal chloride at a temperature of 200°C to 1100°C in an inert gas atmosphere, and ii) Step of extracting and isolating the iron chloride and aluminum chloride formed in the exhaust gas flow. A process for producing iron chloride and aluminum chloride, characterized by including the following:

2. The process according to claim 1, characterized in that the iron chloride is precipitated from the exhaust gas flow by resublimation in step ii).

3. The process according to claim 1, characterized in that the aluminum chloride is precipitated from the exhaust gas flow by resublimation in step ii).

4. The process according to any one of claims 1 to 3, characterized in that the sewage sludge incineration ash contains iron and aluminum compounds in an amount of 1.7% to 41.2% by weight in terms of their respective elemental metals.

5. The process according to any one of claims 1 to 4, characterized in that the reaction is carried out with at least one alkali metal chloride and at least one alkaline earth metal chloride.

6. The process according to any one of claims 1 to 5, characterized in that the reaction is carried out with sodium chloride and magnesium chloride.

7. The process according to any one of claims 1 to 5, characterized in that the reaction is carried out with potassium chloride and magnesium chloride.

8. In terms of each element, the aforementioned sewage sludge incineration ash is 4% to 38% by weight of calcium, 0% to 2% by weight of potassium, 0.1% to 4% by weight of magnesium, 0.1% to 4% by weight of sodium, 4% to 40% by weight of phosphate PO ４ ３－ , 0% to 7% by weight of sulfur, Silicon in an amount of 0% to 24% by weight, 0% to 2% by weight of titanium The process according to any one of claims 1 to 7, characterized by containing

9. The process according to any one of claims 1 to 8, characterized in that a mixture of alkaline earth metal chlorides and alkali metal chlorides is used in a weight ratio of 4:1 to 0.25:1, particularly 2:1 to 0.5:

1.

10. The process according to any one of claims 1 to 9, characterized in that the molar ratio of chlorine derived from the alkali metal chloride and alkaline earth metal chloride used to the total amount of iron and aluminum present in the mixture is 1 to 6 in terms of metal.

11. The process according to any one of claims 1 to 10, characterized in that the reaction is carried out at a temperature of 400°C to 1000°C.

12. A process for producing a water-soluble phosphate compound having a water solubility of more than 1 g / l at 20°C, i) A step of reacting sewage sludge incineration ash containing at least one iron compound and an aluminum compound with at least one alkali metal chloride and / or at least one alkaline earth metal chloride at a temperature of 200°C to 1100°C in an inert gas atmosphere. ii) A step of extracting the iron chloride and aluminum chloride formed in the exhaust gas flow, iii) The obtained residue is treated by adding 0.1 to 5 mol of mineral acid per mol of phosphate in the residue, preferably 0.2 to 1 mol of mineral acid per mol of phosphate in the residue, to obtain a water-soluble phosphate compound. A manufacturing process characterized by including the following.

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