The process of producing iron chloride and aluminum chloride from wastewater sludge ash.

Abstract

DEPCT69 The process of producing iron chloride and aluminum chloride has unique characteristics: The process includes: i) Reaction of wastewater sludge ash containing iron compounds and other compounds. At least one type of aluminum with at least one type of alkali metal chloride and / or chloride. Of at least one alkaline earth metal at a temperature between 200°C and 1100°C. In an atmosphere of inert gases and... ii) Extraction and separation of iron chloride and aluminum chloride generated in the stream. Exhaust gas;

Description

[0001] Process for the production of iron chloride and aluminum chloride from sewage sludge ash

[0002] The invention relates to a process for the production of iron chloride and aluminum chloride from iron and aluminum compounds contained in sewage sludge ash.

[0003] The production of iron chlorides such as Fe(II)Cl2 and Fe(III)Cl3 is usually based on metallic iron. The same applies to aluminum chloride, which is also produced from elemental aluminum. However, there are increasingly large-volume iron- and aluminum-containing compounds that have not previously been considered as alternative sources for the production of the corresponding chlorides, such as sewage sludge ash.

[0004] For some waste materials containing iron-containing compounds, iron is a disruptive element when it comes to the recycling of the main components of these waste streams. This is particularly true of sewage sludge ash, which typically consists of a high single-digit to mid-double-digit percentage of various iron compounds (based on elemental iron). These iron compounds are generally very poorly soluble in water, making their direct use unprofitable. For example, the iron phosphate present in sewage sludge ash is very poorly soluble even in highly concentrated phosphoric acid solutions, which makes the use of phosphate fertilizers highly contaminated with iron ions uneconomical.

[0005] Sewage sludge ash therefore offers itself as an additional source for the production of iron chlorides as well as aluminum chlorides.

[0006] The reaction of phosphates with chlorides of alkali and / or alkaline earth metals has been investigated several times for the application of sewage sludge ash. Sewage sludge ash was mixed with various alkali or alkaline earth chlorides and heated dry in air with the aim of achieving the heavy metal depletion necessary for the direct use of the ash in the agricultural industry.

[0007] For example, Christian Adam et al. (Materials Transactions, Vol. 48, No. 12 (2007) pp. 3056-3061) reported on the dry reaction of sewage sludge ash with magnesium chloride at temperatures up to 1000°C in air. According to Fig. 5, they found virtually complete retention of the iron and aluminum components in the residue, thus observing no depletion of aluminum and iron. Mattenberger et al., in Waste Management 28 (2008) pp. 2709-2722, also conducted experiments on the removal of Cd, Cr, Cu, Ni, Pb, and Zn from sewage sludge ash by adding KCl or MgCl at temperatures above 900°C in air and also reported no depletion of iron or aluminum.

[0008] The object of the invention was therefore to provide a corresponding process based on iron and aluminum compounds contained in sewage sludge ash.

[0009] Surprisingly, a process for the production of iron and aluminum chlorides has now been found, which is characterized in that i) a sewage sludge ash containing at least one iron and aluminum compound is reacted with at least one alkali metal chloride and / or at least one alkaline earth metal chloride at a temperature of 200 to 1100°C in an inert gas atmosphere, preferably containing less than 200 ppm of oxygen, and ii) the iron chloride and aluminum chloride formed are discharged and isolated in the exhaust gas stream.

[0010] Sewage sludge ash

[0011] Sewage sludge ash is preferably understood to refer to both the solid residue resulting from sewage sludge incineration and the solid residue resulting from sewage sludge gasification to produce fuel gas. Sewage sludge ash can contain various components, such as aluminum phosphates, iron phosphates such as calcium iron phosphate (e.g., CaFe(PO4)7) or whitlockite (Ca3(PC>4)2), gypsum, calcium hydroxides, oxides, and carbonates, iron oxides such as hematite (Fe2C>3), quartz (SiO2), and Indialite (Mg2Al4SisOi8), to name just a few.

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

[0013] The sum of iron and aluminum compounds is preferably from 1.7 to 41.2 wt.%, calculated as the respective elemental metal. The preferred composition of a sewage sludge ash contains at least one phosphate source, each with a proportion of at least 1 wt.%, based on the sewage sludge ash.

[0014] The sewage sludge ash may usually contain other typical elements, preferably calculated on the respective element: calcium from 4 to 38 wt.%,

[0015] Potassium from 0 to 2 wt.%,

[0016] Magnesium from 0.1 to 4 wt.%,

[0017] Sodium from 0.1 to 4% by weight

[0018] Phosphate PO4 3 'from 4 to 40 wt.%,

[0019] Sulphur from 0 to 7 wt.%,

[0020] Silicon from 0 to 24 wt% and

[0021] Titanium from 0 to 2 wt%.

[0022] The elements together, calculated as oxides, preferably make up more than 70 wt.% of the sewage sludge ash.

[0023] The respective components can preferably be present as oxides, phosphates, or sulfates. The iron compound is preferably present as an iron(III) compound in an amount of 50-100 wt.%. Preferably, 80 wt.% or more of the phosphates are present as metal phosphates of aluminum, calcium, or iron.

[0024] Sewage sludge ash also contains numerous other elements in minor amounts, primarily copper, zinc, lead, barium, and manganese. The silicon mentioned above is present primarily as sand, primarily from the filtration processes common in sewage treatment plants.

[0025] Alkali chlorides

[0026] Preferred alkali chlorides are NaCl, KCl, LiCl, and mixtures thereof. NaCl or KCl, or a mixture of NaCl and KCl, is preferred. If NaCl is used in a mixture with other alkali chlorides, especially with KCl, the mixing weight ratio is preferably from 10:1 to 0.1:1, in particular from 5:1 to 0.5:1.

[0027] The alkali chloride is preferably used in an amount of 1 to 5 mol, based on 1 mol of the sum of the moles of iron and aluminum present, for example, determined by elemental analysis. The alkali chloride is preferably used in an amount of 5:1 to 1:1 (mol / mol) based on 1 mol of the sum of the moles of iron and aluminum present in the mixture, for example, determined by elemental analysis, for example, performed by ICP-OES or ICP-MS.

[0028] Alkaline earth chlorides

[0029] Suitable alkaline earth chlorides include MgCh, CaCh, or mixtures thereof. MgCh is preferred.

[0030] Preferably, a mixture of alkaline earth metal chlorides and alkali metal chlorides, in particular MgCh and NaCl and / or KCl, is used in a weight ratio of 4:1 to 0.25:1, in particular of 2:1 to 0.5:1. A mixture of KCl, NaCl and MgCh is particularly preferably used.

[0031] Also particularly preferred is a mixture of MgCh and KCl with a weight ratio of 3 : 1 to 0.5 : 1.

[0032] Miscellaneous

[0033] The process is preferably characterized in that the molar ratio of chlorine from the alkali metal chlorides and alkaline earth metal chlorides used to the sum of iron and aluminum present in the mixture, calculated as metal, preferably determined by elemental analysis, for example carried out by ICP-OES or ICP-MS, is 1 to 6.

[0034] If necessary, the thermal conversion step can be preceded by briquetting, pelletizing, or extruding the sewage sludge ash, possibly followed by thermal pretreatment at 100 to 199°C, preferably as a mixture with the corresponding alkali and / or alkaline earth chlorides. For this purpose, auxiliary materials such as phyllosilicates such as bentonite, ligninsulfonate, methylcellulose, water glass, starch, or others can be used.

[0035] Proceedings

[0036] The feedstocks, the sewage sludge ash, the alkali metal chloride(s) and / or alkaline earth metal chloride(s), are preferably mixed in dry form in a mixer. Paddle mixers or mills, such as a ball mill, are preferred as mixers. The latter have the advantage of achieving better homogenization of the reactants through comminution. If necessary, shaping by briquetting, pelletizing, or extrusion follows.

[0037] It is advantageous to carry out the mixing step of the reactants in an inert gas atmosphere, preferably anhydrous, in order to protect the possibly contained hygroscopic components from water absorption, which could have a detrimental effect on the process yield.

[0038] The reaction itself also preferably takes place 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, especially less than 100 ppm, of oxygen.

[0039] The conversion of sewage sludge ash containing iron and aluminum compounds can take place in a fluidized-bed, packed-bed, or moving-bed reactor, in a shaft furnace, or in a preferably gas-tight furnace, which is most easily designed as an indirectly heated tube furnace or rotary kiln. The products formed during the reaction, which are volatile at the reaction temperature, primarily iron chloride, but also aluminum chlorides and possibly other heavy metal chlorides, are preferably resublimed and collected together at a cold location at temperatures below 150°C, or resublimed and collected separately at locations of varying coolness.

[0040] In a preferred embodiment, the iron chloride formed is isolated from the exhaust gas stream by resublimation and the aluminum chloride is isolated from the exhaust gas stream by resublimation.

[0041] Preferred deposition temperatures for FeCh are less than 700°C, in particular less than 700°C to 307°C, for FeCh less than 307°C, in particular 150°C to 300°C and for AlCh less than 150°C, in particular 110°C to 149°C.

[0042] The iron recovered according to the invention in the form of iron(III) chloride and / or iron(II) chloride is already very pure and can then be converted into the desired raw iron form. Examples include iron sulfate, iron nitrate, iron phosphate, or various forms of iron oxide.

[0043] Alternatively, the iron chloride can be introduced directly as a gas stream into an aqueous medium containing sulfuric acid, nitric acid, or phosphoric acid, even without being separated by resublimation, thereby resulting in the formation of the corresponding iron(III) sulfates, nitrates, or phosphates. If necessary, a suitable reducing agent is used in the reaction to obtain iron(II) sulfate, iron(II) nitrate, or iron(II) phosphate.

[0044] However, the separation of iron chloride from the exhaust gas stream by resublimation is preferred.

[0045] Alternatively, the aluminum chloride can be introduced directly as a gas stream into an aqueous medium containing sulfuric acid, nitric acid or phosphoric acid, even without being separated by resublimation, and thereby caused to form corresponding aluminum sulfates, nitrates or phosphates.

[0046] However, the separation of aluminum chloride from the exhaust gas stream by resublimation is preferred.

[0047] The residue after the reaction preferably contains phosphates of the alkali and / or alkaline earth metal group used, as well as possibly other phosphates, such as Ca3(PO4)2.

[0048] The resulting residue is preferably treated by adding 0.1 to 5 mol of phosphoric acid per mol of phosphate, preferably 0.2 to 1 mol of phosphoric acid per mol of phosphate. The reaction residue can thus be converted into a water-soluble salt form, which is suitable for use in agriculture.

[0049] temperature

[0050] The reaction preferably takes place at a temperature of 400 to 1000°C. The reaction typically lasts 5 minutes to 10 hours, preferably 2 to 5 hours.

[0051] Use of the residue

[0052] While natural iron phosphates occur mainly in iron deposits such as magnetic pyrite deposits, sewage sludge ash containing iron phosphate compounds, for example, is produced during the incineration of sewage sludge and consists of a high percentage (up to 40 wt%) of phosphate.

[0053] Sewage sludge ash is typically a mixture of various phosphates, such as calcium, iron, and aluminum phosphate. The exact composition or ratio of the metal cations depends on the technology used by the sewage sludge-producing treatment plants for phosphate precipitation. Iron phosphate, which frequently arises during precipitation processes in sewage treatment plants, is one of the most common phosphate representatives.

[0054] One way to make the phosphate contained in sewage sludge ash available to plants is by digestion with HCl or H2SO4, as described, for example, in EP 3 623 348 B1. This process uses solutions, which leads to a poor space-time yield. Numerous chemicals are used, such as various alkalis, acids, and milk of lime, which make the process complicated and expensive. Filtration steps such as those for iron hydroxide and aluminum hydroxide are technically complex and therefore costly. At the same time, large amounts of waste are generated because the chloride used in the HCl cannot be released as a product.

[0055] Thermal processes are also mentioned, for example, Christian Adam et al. (Materials Transactions, Vol. 48, No. 12 (2007) pp. 3056 - 3061).

[0056] The invention therefore also relates to a process for the production of water-soluble phosphate compounds having a water solubility at 20 °C of greater than 1 g / l, characterized in that i) a sewage sludge ash containing at least one iron and aluminum compound is reacted with at least one alkali metal chloride and / or at least one alkaline earth metal chloride at a temperature of 200 to 1100 °C in an inert gas atmosphere, preferably containing less than 200 ppm of oxygen, ii) the iron chloride and aluminum chloride formed are discharged in the exhaust gas stream, and iii) the residue obtained is treated to give water-soluble phosphate compounds by adding 0.1 to 5 mol of a mineral acid per mole of phosphate in the residue, preferably 0.2 to 1 mol of a mineral acid per mole of phosphate in the residue.

[0057] Examples of mineral acids used in step iii) include sulfuric acid, hydrochloric acid, nitric acid and / or phosphoric acid, with phosphoric acid being preferred.

[0058] The residue of the reaction can thus be converted according to step iii) into a water- and / or citric acid-soluble salt, which as such is suitable for use in agriculture.

[0059] The preferred ranges for this process also correspond to those already stated above. Reactor

[0060] The material to be used in the process according to the invention is preferably introduced into a reactor, which is preferably provided with a layer resistant to the reaction conditions to be established. Preferred reactor materials are nickel- or graphite-coated reactors. Tubular reactors such as rotary tube reactors or other reactors can be used as such. Particular preference is given to reactors that allow movement of the material during the reaction in order to enable the most effective contact of the reactants and heat distribution. Fluidized bed reactors, rotary tube reactors, or a reaction in an extruder device with screw propulsion are preferred.

[0061] In the case of a tubular reactor, the reactor length is preferably 0.2 to 40 m. The residence time in the reactor during the reaction generally depends on the temperature and the contact potential of the reactants. The residence time in the reactor can range, for example, from one minute to five hours. The process according to the invention can be operated batchwise or continuously.

[0062] Examples

[0063] Analytics

[0064] After dissolving the sewage sludge ash sample in suitable acids, the analysis was carried out in an ICP-OES, after calibration for the respective element using calibrated standard solutions of the respective elements.

[0065] X-ray diffraction patterns (XRD) were recorded on powders (flat bed) at 2 theta angles between 0 and 60° with a wavelength of 0.154 nm.

[0066] Example 1 :

[0067] 6.8g sewage sludge ash (according to XRD, contains iron-phosphorus compounds, including CaFe(PO4)7, with the composition (in weight percent): 13% Fe, 1.5% Al, 6.8% Ca, 0.44% Mg, 21% PO4 3 A solution of ferric chloride (0.52% Na) is mixed with 1.4g KCl, 3.6g MgCl, and 1.6g NaCl. The solution is then heated to 450°C in a crucible open to an anhydrous atmosphere and held at this temperature for 4 hours. The solution is then heated to 1000°C and held for a further 4 hours. A weight loss of 21% was observed, which is due to the sublimation of ferric chloride and aluminum chloride.

[0068] In order to also utilize the residue, the reaction time was extended, resulting in an iron-free residue that can be used in agriculture.

[0069] The residue obtained shows characteristic reflections in the X-ray diffractogram located at 32.3° 2Theta and 33.2° 2Theta (wavelength: 1.54060 Angstroms).

[0070] The resulting residue is treated with 1.4 g of phosphoric acid to convert the resulting magnesium phosphate and calcium phosphate into their water-soluble forms. The powder is granulated and has a combined iron and aluminum content of less than 1 wt%, calculated as elements.

[0071] Example 2:

[0072] 69g sewage sludge ash (according to XRD contains among other things CaFe(PO4)7, with the composition (in weight percent) 13% Fe, 1.5% AI, 6.8% Ca, 0.44% Mg, 21% PO4 3; 0.52% Na) are thoroughly ground with 14g NaCl and 17g MgCh (anhydrous). 56.2g of the red mixture are filled into a quartz tube, which is immediately flushed with dry nitrogen to prevent the absorption of water from the air. The quartz tube is placed in a tube furnace. During heating, a motor rotates the quartz tube in an oscillating manner at a rate of approximately 2007min around its own axis, so that the powder bed is continuously in motion. Simultaneously, a gas stream of 0.5l / min of purified nitrogen (oxygen <200ppm v / v) is passed through the tube and thus also over the sample. The tube outlet (=gas outlet) is narrowed by a loosely inserted piece of quartz wool.

[0073] The furnace and the sample in the quartz tube are heated to 1000°C (20 K / min) while maintaining the gas flow and oscillating rotation. After 120 minutes, the experiment is terminated, and the furnace and sample are cooled to room temperature under continued nitrogen flow. The originally red powder has turned white (47.2 g). At the same time, a yellowish precipitate has formed at the reactor outlet in the region above 200°C, and a white sublimate has formed in the cooler region farther from the furnace, at approximately 100°C. A gas has been produced that consists at least partially of HCl, as confirmed by gas-phase infrared spectroscopy.

[0074] The white residue remaining in the tube (yield 47.2 g or 84%) was analyzed. Based on the initial mixture, only 41% of the Fe, 64% of the Al, 61% of the Mg, and 72% of the Na were recovered.

[0075] In order to also utilize the residue, the reaction time is extended, resulting in an iron-free and aluminum-free residue that can be used in agriculture.

[0076] The phosphorus and calcium content of the sample remain unchanged by the reaction. The resulting residue exhibits characteristic reflections in the X-ray diffraction pattern located at 32.3° 2Theta and 33.2° 2Theta (wavelength: 1.54060 angstroms).

[0077] The resulting residue is mixed with 50g of 85% phosphoric acid to convert the resulting magnesium phosphate and calcium phosphate into their water-soluble forms. The resulting mixture can be used for plant fertilization, optionally after granulation.

[0078] The white resublimate obtained is aluminum chloride, the yellowish resublimate is ferric chloride, both of which can be collected separately and both are of high purity.

[0079] Example 3:

[0080] 6.8g sewage sludge ash (according to XRD contains among other things CaFe(PO4)7, with the composition (in weight percent): 13% Fe, 1.5% AI, 6.8% Ca, 0.44% Mg, 21% PO4 3; 0.52% Na) is mixed with 1.8 g MgCh and 3.2 g KCl. The red mixture is filled into a quartz tube, which is immediately purged with dry nitrogen to prevent the absorption of water from the air. The quartz tube is placed in a tube furnace and sufficiently purged with purified nitrogen (0.5 l / min, oxygen <200 ppm v / v) for half an hour. During the experiment and the temperature rise due to the furnace heating, the gas flow of 0.5 l / min of purified nitrogen (oxygen <200 ppm v / v) is maintained through the tube and the sample. The empty tube outlet protruding from the furnace (=gas outlet) is kept at 100°C and the mixture in the glass tube is heated to 750°C in the furnace.

[0081] The originally red powder has turned white, and at the same time, a yellowish precipitate has formed at the reactor outlet in the region above 200°C, and a white sublimate has formed in the cooler region farther from the furnace, at approximately 100°C. The resulting white sublimate is aluminum chloride, and the yellowish sublimate is ferric chloride. Both can be collected separately and are of high purity.

[0082] The phosphorus and calcium amounts in the sample remain unchanged by the reaction. The resulting residue is treated with 50 g of 85% phosphoric acid to convert the resulting magnesium phosphate and calcium phosphate into their water-soluble forms. The resulting mixture can be used for plant fertilization, if necessary after granulation.

[0083] The sublimate also obtained can, if necessary after purification of unwanted heavy metals, be reused for phosphate precipitation in sewage treatment plants.

Claims

DEPCT691. The characteristic process of iron chloride and aluminum chloride production is characterized by the inclusion of i) the reaction of wastewater sludge ash containing at least one iron and aluminum compounds with at least one alkali metal chloride and / or at least one alkaline earth metal chloride at temperatures of 200°C to 1100°C in an inert gas atmosphere and ii) the extraction and separation of iron chloride and aluminum chloride generated in the waste gas stream.

2. The characteristic process of claim 1 is characterized by the accumulation of iron chloride from the waste gas stream by reverse sublimation in step ii).

3. The characteristic process of claim 1 is characterized by the accumulation of aluminum chloride from the waste gas stream by reverse sublimation in step ii).

4. At least one of the processes of claims 1 through 3 is characterized by the wastewater sludge ash containing iron and aluminum compounds in amounts ranging from 1.7% to 41.2% by weight of each elemental metal. 5.

6. At least one of the processes described in claims 1 through 4, characterized by the reaction being carried out with at least one alkali metal chloride and at least one alkaline earth metal chloride.

7. At least one of the processes described in claims 1 through 5, characterized by the reaction being carried out with sodium chloride and magnesium chloride.

8. At least one of the processes described in claims 1 through 5, characterized by the reaction being carried out with potassium chloride and magnesium chloride.

9. At least one of the processes described in claims 1 through 7, characterized by the fact that, as calculated for each element, the ash of wastewater sludge contains the following elements: calcium from 4% to 38% by weight, potassium from 0% to 2% by weight, magnesium from 0.1% to 4% by weight, sodium from 0.1% to 4% by weight, phosphate (PO4^3) from 4% to 40% by weight, sulfur from 0% to 7% by weight, silicon from 0% to 24% by weight, and titanium from 0% to 2% by weight.The process according to at least one of the claims 1 through 8 is characterized by the use of a mixture of alkali earth metal chlorides and alkali metal chlorides in a weight ratio of 4:1 to 0.25:1, particularly from 2:1 to 0.5:

1. The process according to at least one of the claims 1 through 9 is characterized by the molar ratio of chloride from alkali metal chlorides and alkali earth metal chlorides used to the sum of iron and aluminum present in the calculated metal alloy being 1 to 6. The process according to at least one of the claims 1 through 10 is characterized by the reaction being carried out at temperatures of 400°C to 1000°C.The process of producing water-soluble phosphate compounds with a solubility of more than 1 g / L at 20°C is characterized by the following components: i) the reaction of wastewater sludge ash containing at least one iron and aluminum compound with at least one alkali metal chloride and / or at least one alkaline earth metal chloride at temperatures of 200°C to 1100°C in an inert gas atmosphere; ii) the extraction of iron chloride and aluminum chloride generated in the waste gas stream; and iii) conditioning the resulting residue by adding 0.1 to 5 mol / mol / 1 mol / 2 ...