Method for preparing polyaluminum chloride product for drinking water treatment

Abstract

The present invention relates to a method for preparing a polyaluminum chloride (PAC) product for drinking water treatment. The method of the present invention comprises the following steps: a) providing a PAC-containing liquid raw material; b) adding calcium aluminate substantially free of SiO2 into the PAC-containing liquid raw material; and c) optionally, carrying out filtering to obtain a liquid PAC product. The PAC product prepared with the method of the present invention has a high concentration of Al2O3, high basicity, and high stability.

Description

Method for preparing polyaluminium chloride product for drinking water treatment Technical Field

[0001] The present invention relates to the field of drinking water treatment, and in particular to a method for preparing a high-concentration, high-basicity polyaluminium chloride product for drinking water treatment using calcium aluminate, and a product prepared according to the method. Background Art

[0002] Polyaluminum chloride (PAC) is an inorganic polymer flocculant currently used in water treatment. Upon application to the water being treated, PAC forms a polynuclear hydroxyaluminum complex, which flocculates insoluble particulate matter in the water through, for example, electrical neutralization. Alumina (Al2O3) content and basicity (also known as alkalinity) are important indicators of PAC products. A high alumina content or high basicity is desirable.

[0003] PAC is typically produced using either a one-step or two-step process. The one-step process involves contacting aluminum-containing materials (e.g., calcium aluminate, bauxite, aluminum chips, aluminum ash, and aluminum slag) with an acid (e.g., hydrochloric acid). However, the one-step process is difficult to produce high-quality (i.e., drinking water treatment grade) PAC. The two-step process involves contacting the aluminum-containing materials with an acid in the first step, followed by the addition of an additional base (e.g., NaCO3, NaOH, etc.) to increase the basicity in the second step.

[0004] Calcium aluminate is a common raw material used in the production of polyaluminium chloride. While its chemical formula can be written as CaO·Al₂O₃, commercially available calcium aluminate typically comes from solid waste residues from other industries and is therefore a complex mixture of various components. The main components of calcium aluminate typically include Al₂O₃ (47-55 wt%), CaO (25-35 wt%), SiO₂ (5-10 wt%), Fe₂O₃ (1-6 wt%), TiO₂ (2-5 wt%), MgO (1-2 wt%), and heavy metals such as lead (see "Inorganic Polymer Flocculation Theory and Flocculants," by Tang Hongxiao, China Architecture & Building Press, 1st edition, August 2006). The Chinese national standard for calcium aluminate for water treatment (GB / T 29341-2022 Calcium Aluminate for Water Treatment Agents) only specifies the Al₂O₃, CaO, and heavy metal contents in calcium aluminate, but does not specify the contents of other components.

[0005] To obtain a product with a high alumina content, the production process must address the problem of high viscosity of the reaction system caused by the presence of a large amount of aluminum (i.e., high aluminum concentration). To overcome this high viscosity, acid must be added, but the addition of acid hinders the achievement of high basicity. Similarly, to obtain a product with a high basicity, the amount of acid added must be controlled, which ultimately leads to a low alumina content. How to simultaneously increase the basicity and concentration of polyaluminum chloride products has been a problem that those skilled in the art have long sought to solve.

[0006] Summary of the Invention

[0007] The present invention provides a method for preparing a polyaluminium chloride product. The polyaluminium chloride product prepared by the method has high Al2O3 concentration, high basicity, high stability and low impurity content, and can be used for treating drinking water.

[0008] In one embodiment, the method of the present invention comprises the following steps:

[0009] a) providing a liquid raw material containing PAC;

[0010] b) adding calcium aluminate substantially free of SiO2 to the PAC-containing liquid feedstock;

[0011] c) optionally filtering to obtain a liquid polyaluminium chloride product.

[0012] In one embodiment, the method of the present invention further comprises step d):

[0013] The obtained liquid polyaluminium chloride product is dried to obtain a solid polyaluminium chloride product. In a preferred embodiment, the drying is spray drying.

[0014] In one embodiment, in step a), the PAC-containing liquid raw material is prepared using a raw material that is substantially free of SiO2.

[0015] In one embodiment, in step a), the PAC-containing liquid feedstock is prepared using raw materials comprising aluminum hydroxide and hydrochloric acid.

[0016] In one embodiment, in step a), the PAC-containing liquid raw material comprises 10 wt% to 20 wt% of Al2O3. In a preferred embodiment, in step a), the PAC-containing liquid raw material comprises 10 wt% to 20 wt% of Al2O3, for example, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 11.10, 11.111, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 11.112, 11. .8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 13.0, 13.1, 13.2, 13.3, 13.4, 13.5, 13.6, 13.7, 13.8, 13.9, 14.0, 14.1, 14.2, 14.3, 14.4, 14.5, 14.6 , 14.7, 14.8, 14.9, 15.0, 15.1, 15.2, 15.3, 15.4, 15.5, 15.6, 15.7, 15.8, 15.9, 16.0, 16.1, 16.2, 16.3, 16.4, 16.5, 16.6, 16.7, 16.8, 16.9, 17.0, 17.1, 17.2, 17.3, 17.4, 1 %, or a subrange consisting of any value within these ranges.

[0017] In one embodiment, in step a), the basicity of the PAC-containing liquid feedstock is 30-50%, for example, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50%, or a sub-range consisting of any value within these ranges.

[0018] In one embodiment, step a) further comprises diluting the provided PAC-containing liquid feedstock under conditions of optional stirring and / or optional heating. In a preferred embodiment, the stirring rate is 100-10000 rpm, for example, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000 rpm, or a sub-range consisting of any value within these ranges. In a preferred embodiment, the temperature of the heating condition is 80-120°C, for example, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120°C, or a sub-range consisting of any value in these ranges.

[0019] In one embodiment, step b) is further carried out under stirring. In a preferred embodiment, the stirring rate is 100-10000 rpm, for example 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000 rpm, or a sub-range consisting of any value in these ranges. In a preferred embodiment, step b) is carried out at a temperature of 80-120°C, for example 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120°C, or a sub-range consisting of any value in these ranges. In a preferred embodiment, step b) lasts for 1-5 hours, such as 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 hours, or a subrange consisting of any value within these ranges.

[0020] In one embodiment, the substantially SiO2-free calcium aluminate comprises less than or equal to 1 wt% SiO2, e.g., less than or equal to 0.95 wt%, less than or equal to 0.9 wt%, less than or equal to 0.85 wt%, less than or equal to 0.8 wt%, less than or equal to 0.75 wt%, less than or equal to 0.7 wt%, less than or equal to 0.65 wt%, less than or equal to 0.6 wt%, less than or equal to 0.55 wt%, less than or equal to 0.5 wt%, less than or equal to 0.45 wt%, less than or equal to 0.4 wt%, less than or equal to 0.35 wt%, less than or equal to 0.3 wt%, less than or equal to 0.25 wt%, less than or equal to 0.2 wt%, less than or equal to 0.15 wt%, less than or equal to 0.1 % by weight, less than or equal to 0.09 wt %, less than or equal to 0.08 wt %, less than or equal to 0.07 wt %, less than or equal to 0.06 wt %, less than or equal to 0.05 wt %, less than or equal to 0.04 wt %, less than or equal to 0.03 wt %, less than or equal to 0.02 wt %, less than or equal to 0.01 wt %, less than or equal to 0.009 wt %, less than or equal to 0.008 wt %, less than or equal to 0.007 wt %, less than or equal to 0.006 wt %, less than or equal to 0.005 wt %, less than or equal to 0.004 wt %, less than or equal to 0.003 wt %, less than or equal to 0.002 wt %, less than or equal to 0.001 wt %, or sub-ranges consisting of any values ​​within these ranges.

[0021] In one embodiment, the substantially SiO2-free calcium aluminate comprises greater than or equal to 60 wt% Al2O3, for example, 60 wt%, 61 wt%, 62 wt%, 63 wt%, 64 wt%, 65 wt%, 66 wt%, 67 wt%, 68 wt%, 69 wt%, 70 wt%, 71 wt%, 72 wt%, 73 wt%, 74 wt%, 75 wt%, 76 wt%, 77 wt%, 78 wt%, 79 wt%, 80 wt%, or a subrange consisting of any value within these ranges.

[0022] In one embodiment, the substantially SiO2-free calcium aluminate comprises 25-35 wt% CaO, e.g., 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, or a sub-range consisting of any value within these ranges.

[0023] In one embodiment, the substantially SiO2-free calcium aluminate comprises less than or equal to 0.2 wt% Fe2O3, e.g., less than or equal to 0.15 wt%, less than or equal to 0.1 wt%, less than or equal to 0.05 wt%, less than or equal to 0.04 wt%, less than or equal to 0.03 wt%, less than or equal to 0.02 wt%, less than or equal to 0.01 wt%, or sub-ranges consisting of any value within these ranges.

[0024] The calcium aluminate substantially free of SiO2 described herein is commercially available or prepared using raw materials substantially free of SiO2. In one embodiment, the calcium aluminate substantially free of SiO2 described herein is calcium aluminate cement, preferably high calcium aluminate cement, more preferably pure calcium aluminate cement.

[0025] In one embodiment, the substantially SiO2-free calcium aluminate described herein is added in powder form. In another embodiment, the substantially SiO2-free calcium aluminate described herein is added in slurry form, such as a 40-80 wt% slurry, preferably a 50 wt% slurry.

[0026] In one embodiment, in step c), before optional filtration, the solution is cooled to a temperature that the filtration equipment can withstand, for example, any temperature below 80°C, or, for example, room temperature. In a preferred embodiment, in step c), the solution is cooled to 20-80°C, for example, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80°C, or a sub-range consisting of any value within these ranges.

[0027] In a preferred embodiment, in step c), filter paper is used for filtration, preferably glass fiber filter paper, such as that of catalog number 1820-125. GF / A glass fiber filter paper.

[0028] In a preferred embodiment, in step c), filtration is performed using a filter press, for example, a plate and frame filter press.

[0029] In one embodiment, the basicity of the liquid polyaluminium chloride product is 60-90%, for example, 60.0, 60.5, 61.0, 61.5, 62.0, 62.5, 63.0, 63.5, 64.0, 64.5, 65.0, 65.5, 66.0, 66.5, 67.0, 67.5, 68.0, 68.5, 69.0, 69.5, 70.0, 70.5, 71.0, 71.5, 72.0, 72.5, 73.0, 73.5, 74.0, 74.5, 75.0, 75.5, 76.0, 76.5, 77.0, 77.5, 78.0, 78.5, 79.0, 79.5, 80.0, 80.5, 81.0, 81.5, 82.0, 82.5, 83.0, 83.5, 84.0, 84.5, 85.0, 85.5, 86.0, 86.5, 87.0, 87.5, 88.0, 88.5, 89.0, 89.5, 90.0%, or a sub-range consisting of any value within these ranges.

[0030] In one embodiment, the liquid polyaluminium chloride product comprises greater than or equal to 10 wt% Al2O3, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, 11.1, 11.2, 11.3, 11.4, 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6, 12.7, 12.8, 12.9, 13.0, 13.1, 13. 2, 13.3, 13.4, 13.5, 13.6, 13.7, 13.8, 13.9, 14.0, 14.1, 14.2, 14.3, 14.4, 14.5, 14.6, 14.7, 14.8, 14.9, 15.0, 15.1, 15.2, 15.3, 15.4, 15.5, 15.6, 15.7, 15.8, 15.9, 16.0, 16.1, 16.2, 16.3, 16.4, 16.5, 16.6, 16.7, 16.8, 16.9, 17.0, 17.1, 17.2, 17.3, 17.4, 17.5, 17.6, 17.8, 17.9, 18, 18.1, 18.2, 18.3, 18.4, 18.5, 18.6, 18.7, 18.8, 18.9, 19.0, 19.1, 19.2, 19.3, 19.4, 19.5, 19.6, 19.7, 19.8, 19.9, 20.0, 20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8, 20.9, 21.0, 21.1, 21.2, 21.3, 21.4 %, 21.5%, 21.6%, 21.7%, 21.8%, 21.9%, 22.0%, 22.1%, 22.2%, 22.3%, 22.4%, 22.5%, 22.6%, 22.7%, 22.8%, 22.9%, 23.0%, 23.1%, 23.2%, 23.3%, 23.4%, 23.5%, 23.6%, 23.7%, 23.8%, 23.9%, 24.0%, 24.1%, 24.2%, 24.3%, 24.4%, 24.5%, 24.6%, 24.7%, 24.8%, 24.9%, 25.0%, or a sub-range consisting of any value within these ranges.

[0031] In a preferred embodiment, the liquid polyaluminium chloride product comprises 10-22 wt% Al2O3 and a basicity of 65-85%. Further preferably, the final PAC product comprises 20-22 wt% (e.g., 20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8, 20.9, 21, 21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7, 21.8, 21.9 or 22%, or a sub-range consisting of any value within these ranges) Al2O3 and a basicity of 65-85%, e.g., 65, 65.1, 65.2, 65.3, 65.4, 65.5, 65.6, 65.7, 65.8, 65.9, 66.1, 66.2, 66.3, 66.4, 66.5, 66.6, 66.7, 66.8, 66.9, 67.1, 67.2, 67.3, 67.4, 67.5, 67.6, 67.9, 67.1 65.8, 65.9, 66, 66.1, 66.2, 66.3, 66.4, 66.5, 66.6, 66.7, 66.8, 66.9, 67, 67.1, 67.2, 67.3, 67.4, 67.5, 67.6, 67.7, 67.8, 67.9, 68, 68.1, 68.2, 68.3, 68.4, 68.5, 68.6, 68.7, 68.8, 68.9, 69, 69.1, 69.2, 69.3, 69.4, 69.5, 69.6 , 69.7, 69.8, 69.9, 70, 70.1, 70.2, 70.3, 70.4, 70.5, 70.6, 70.7, 70.8, 70.9, 71, 71.1, 71.2, 71.3, 71.4, 71.5, 71.6, 71.7, 71.8, 71.9, 72, 72.1, 72.2, 72.3, 72.4, 72.5, 72.6, 72.7, 72.8, 72.9, 73, 73.1, 73.2, 73.3, 73.4, 73.5 , 73.6, 73.7, 73.8, 73.9, 74, 74.1, 74.2, 74.3, 74.4, 74.5, 74.6, 74.7, 74.8, 74.9, 75, 75.1, 75.2, 75.3, 75.4, 75.5, 75.6, 75.7, 75.8, 75.9, 76, 76.1, 76.2, 76.3, 76.4, 76.5, 76.6, 76.7, 76.8, 76.9, 77, 77.1, 77.2, 77.3, 77. 4, 77.5, 77.6, 77.7, 77.8, 77.9, 78, 78.1, 78.2, 78.3, 78.4, 78.5, 78.6, 78.7, 78.8, 78.9, 79, 79.1, 79.2, 79.3, 79.4, 79.5, 79.6, 79.7, 79.8, 79.9, 80, 80.1, 80.2, 80.3, 80.4, 80.5, 80.6, 80.7, 80.8, 80.9, 81, 81.1, 81.2, 81.3, 81.4, 81.5, 81.6, 81.7, 81.8, 81.9, 82, 82.1, 82.2, 82.3, 82.4, 82.5, 82.6, 82.7, 82.8, 82.9, 83, 83.1, 83.2, 83.3, 83.4, 83.5, 83.6, 83.7, 83.8, 83.9, 84, 84.1, 84.2, 84.3, 84.4, 84.5, 84.6, 84.7, 84.8, 84.9, or 85%, or a subrange consisting of any value within these ranges.

[0032] In one embodiment, the liquid polyaluminum chloride product contains less than or equal to 0.05 wt% Si, e.g., less than or equal to 0.04 wt%, less than or equal to 0.03 wt%, less than or equal to 0.02 wt%, less than or equal to 0.01 wt%, less than or equal to 0.005 wt%, less than or equal to 0.001 wt%, or a sub-range consisting of any value within these ranges.

[0033] In one embodiment, the liquid polyaluminum chloride product contains less than or equal to 100 ppm Fe, e.g., less than or equal to 90 ppm, less than or equal to 80 ppm, less than or equal to 70 ppm, less than or equal to 60 ppm, less than or equal to 50 ppm, less than or equal to 40 ppm, less than or equal to 30 ppm, less than or equal to 20 ppm, less than or equal to 10 ppm, or a sub-range consisting of any value within these ranges.

[0034] The method of the present invention is simple and easy to control, and can be customized to produce PAC with a predetermined basicity. The method of the present invention can produce products with very high Al2O3 concentrations (e.g., Al2O3 > 20%) and / or high basicity. The PAC products produced by the method of the present invention are highly stable and do not require the addition of stabilizers. The PAC products produced by the method of the present invention can be used for drinking water treatment. After treatment with the PAC products produced by the method of the present invention, the residual aluminum in the treated water is significantly lower than the reference value.

[0035] Unless otherwise specified, the percentages, proportions, ratios, contents or parts described herein are by weight.

[0036] The term "substantially free" as used in the present invention means that the content is less than 1% (by weight) or the specified amount.

[0037] The "room temperature" mentioned in the present invention refers to a temperature of 10-35°C, preferably 20-25°C.

[0038] The "polyaluminium chloride product" of the present invention can be provided in liquid or solid form.

[0039] In the present invention, the concentration (i.e., Al2O3 wt%) and basicity of the polyaluminium chloride product are determined according to conventional methods in the art. The concentration of the liquid polyaluminium chloride product is the mass percentage of Al2O3 in the liquid polyaluminium chloride product; the concentration of the solid polyaluminium chloride product is the mass percentage of Al2O3 in the solid polyaluminium chloride product. DETAILED DESCRIPTION

[0040] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples. The experimental procedures described in the following examples are all conventional procedures unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0041] Example 1

[0042] Preparation of 1kg high basicity polyaluminium chloride product:

[0043] a) 364.9 g of a PAC-containing liquid raw material (PAX 10, a medium-basicity PAC available on the market, produced by reacting Al(OH)3 with HCl. It contains 10 wt% Al2O3 and has a basicity of 40%; the source and composition of this raw material in the following Examples 2-3 and Comparative Examples 1-3 are identical to those in Example 1); 569.9 g of water is added to the PAC-containing liquid raw material, and the mixture is stirred at 260 rpm; the mixture is heated to 90°C with continuous stirring;

[0044] b) adding 65.2 g of substantially SiO2-free calcium aluminate (a commercially available product containing 0.21 wt% SiO2, 68.9 wt% Al2O3, 27.7 wt% CaO, and 0.12 wt% Fe2O3; the sources and composition of this raw material in Examples 2-3 below are identical to those in Example 1) to the above liquid, stirring continuously, and maintaining the temperature at 90°C for 2.5 hours; and cooling the solution to room temperature;

[0045] c) Pass The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0046] Analysis showed that the obtained liquid polyaluminium chloride product contained 10.0 wt% of Al2O3 and had a basicity of 76.3%.

[0047] Example 2

[0048] Preparation of 1kg of high-concentration, high-basicity polyaluminium chloride product for drinking water treatment:

[0049] a) Take 610.6 g of PAC-containing liquid raw material; add 272.4 g of water to the PAC-containing liquid raw material, stir at 260 rpm; heat to 90°C and continue stirring;

[0050] b) adding 117.0 g of calcium aluminate substantially free of SiO2 to the above liquid, stirring continuously, maintaining the temperature at 90°C for 2.5 hours; and cooling the solution to room temperature;

[0051] c) Pass The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0052] The obtained liquid polyaluminium chloride product was analyzed to contain 18.4 wt% Al2O3 and a basicity of 75%.

[0053] Example 3

[0054] Preparation of 1kg of extremely high concentration, high basicity polyaluminium chloride product for drinking water treatment:

[0055] a) taking 678.4 g of a PAC-containing liquid raw material; adding 191.6 g of water to the PAC-containing liquid raw material, stirring at 260 rpm; heating to 90° C., and continuing stirring;

[0056] b) adding 130 g of calcium aluminate substantially free of SiO2 to the above liquid, stirring continuously, maintaining the temperature at 90°C for 2.5 hours; and cooling the solution to room temperature;

[0057] c) Pass The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0058] The obtained liquid polyaluminium chloride product was analyzed to contain 21.7 wt% Al2O3 and a basicity of 70.3%.

[0059] Comparative Example 1

[0060] Preparation of 1 kg of high basicity polyaluminium chloride product for drinking water treatment:

[0061] a) taking 386.4 g of a PAC-containing liquid raw material; adding 545.1 g of water to the PAC-containing liquid raw material, stirring at 260 rpm; heating to 90° C., and continuing stirring;

[0062] b) adding 68.5 g of calcium aluminate powder for ordinary water treatment (commercially available, containing 7.1 wt % SiO 2 , 54.7 wt % Al 2 O 3 , 31.6 wt % CaO, and 1.6 wt % Fe 2 O 3 ; the sources and composition of the raw materials in the following Comparative Examples 2-3 are identical to those in Comparative Example 1) to the above liquid, stirring continuously, maintaining the temperature at 90° C. for 2.5 hours; and cooling the solution to room temperature;

[0063] c) Pass The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0064] Analysis showed that the obtained liquid polyaluminium chloride product contained 10.5 wt% of Al2O3 and had a basicity of 70.2%.

[0065] Comparative Example 2

[0066] Preparation of 1kg of high-concentration, high-basicity polyaluminium chloride product for drinking water treatment:

[0067] a) taking 648.4 g of a PAC-containing liquid raw material; adding 228.2 g of water to the PAC-containing liquid raw material, stirring at 260 rpm; heating to 90° C., and continuing stirring;

[0068] b) adding 123.4 g of calcium aluminate powder for ordinary water treatment to the above liquid, stirring continuously, maintaining the temperature at 90° C. for 2.5 hours; and cooling the solution to room temperature;

[0069] c) Pass The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0070] The obtained liquid polyaluminium chloride product was analyzed to contain 18.7 wt% Al2O3 and a basicity of 69.4%.

[0071] Comparative Example 3

[0072] Preparation of 1kg of extremely high concentration, high basicity polyaluminium chloride product for drinking water treatment:

[0073] a) taking 720 g of a PAC-containing liquid raw material; adding 142 g of water to the PAC-containing liquid raw material, stirring at 260 rpm; heating to 90° C., and continuing stirring;

[0074] b) adding 137 g of calcium aluminate powder for ordinary water treatment to the above liquid, stirring continuously, maintaining the temperature at 90° C. for 2.5 hours; and cooling the solution to room temperature;

[0075] c) Pass The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0076] The obtained liquid polyaluminium chloride product was analyzed to contain 21.8 wt% Al2O3 and a basicity of 69.6%.

[0077] Comparative Example 4

[0078] PAC_2009 is a commercially available high-basicity PAC product containing 10.9 wt% Al2O3 and a basicity of 66.2%.

[0079] Comparative Example 5

[0080] PAX-HB800 is a commercially available high-basicity PAC produced by adding sodium carbonate to medium-basicity PAC. It contains no stabilizer, which compromises the sample's stability (short shelf life). It contains 11.1 wt% Al2O3 and has a basicity of 69.1%.

[0081] Comparative Example 6

[0082] PAX-HB9 is a commercially available high-basicity PAC produced by adding sodium carbonate to medium-basicity PAC. It also contains some divalent anions to enhance performance in applications. However, it contains no stabilizers. It contains 9.1 wt% Al2O3 and has a basicity of 70.7%.

[0083] Comparative Example 7

[0084] PAX-HB10 is a commercially available high-basicity PAC produced by adding sodium carbonate to medium-basicity PAC. It also contains some divalent anions to enhance performance during use. It also contains some stabilizers to improve product stability. It contains 10.1 wt% Al2O3 and has a basicity of 76.8%.

[0085] Comparative Example 8

[0086] PAX-HB1, a commercially available high-basicity PAC produced by adding calcium carbonate to medium-basicity PAC, contains 10.7 wt% Al2O3 and has a basicity of 65.7%.

[0087] Comparative Example 9

[0088] PAX 10 is a commercially available medium basicity PAC produced by reacting Al(OH)3 with HCl. It contains 10.0 wt% Al2O3 and has a basicity of 40%.

[0089] The liquid polyaluminium chloride products obtained in the above examples and comparative examples were subjected to various performance tests, and the specific results are shown in the following Tables 1-5.

[0090] Test Example 1

[0091] The liquid polyaluminium chloride products obtained in the above examples and comparative examples were stored at 50°C and their stability was monitored by visual observation. Specifically, the formation of precipitation was observed with the naked eye and the elapsed time was recorded. The results are shown in Table 1 below.

[0092] Table 1 Stability of liquid polyaluminium chloride products

[0093] Table 1 shows that compared with the liquid polyaluminium chloride product in Comparative Example 9, the liquid polyaluminium chloride product in Example 1 has better stability.

[0094] Test Example 2

[0095] Residual aluminum is regulated as a drinking water quality standard. The aluminum concentration limit in drinking water is 0.2 mg / L (China GB 5749-2022 Drinking Water Hygiene Standard). Aluminum exists in all natural waters, but drinking water contains additional aluminum due to the use of aluminum-based flocculants such as PAC. If the basicity is higher, the flocculation effect is better and the residual aluminum in the water will be lower. The test method used in Test Example 2 is inductively coupled plasma optical emission spectrometry (ICP-OES), and the instrument used is an inductively coupled plasma optical emission spectrometer (model: Avio 200, manufacturer: PerkinElmer).

[0096] The liquid polyaluminium chloride products obtained in the above examples and comparative examples were used to treat surface water from a drinking water treatment plant, where surface water #1 was reservoir water and surface water #2 was river water. The results are shown in Table 2 below.

[0097] Table 2 Residual aluminum content

[0098] Table 2 shows that the residual aluminum content in the surface water treated with the liquid polyaluminum chloride product in the example is lower than that in the surface water treated with the liquid polyaluminum chloride product in the comparative example.

[0099] Test Example 3

[0100] There is a close correlation between dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm (UVA 254nm) in natural water bodies. Therefore, UVA 254nm is often used as a general indicator of organic loading and water quality. The test method used in Test Example 3 is ultraviolet spectrophotometry, and the instrument used is a UV-visible spectrophotometer (Model: UV2550, Manufacturer: Shimadzu).

[0101] The liquid polyaluminium chloride products obtained in the above examples and comparative examples were used to treat reservoir water from a drinking water treatment plant. The UV absorbance of the water before treatment at 254 nm was 0.087. The results are shown in Table 3 below.

[0102] Table 3 Ultraviolet absorbance of treated water at 254nm

[0103] Table 3 shows that compared with the reservoir water treated with the liquid polyaluminium chloride product in the comparative example, the reservoir water treated with the liquid polyaluminium chloride product in the example has a lower ultraviolet absorbance at 254nm, which means that its organic carbon concentration is lower and the water quality is better.

[0104] Test Example 4

[0105] The viscosity of the liquid polyaluminum chloride products obtained in the above examples and comparative examples was tested. The results are shown in Table 4 below. The test method used in Test Example 3 was dynamic viscosity, and the instrument used was a rotational viscometer (Model: LVDV-1 Prime, Manufacturer: Brookfield).

[0106] Table 4 Viscosity of liquid polyaluminium chloride products

[0107] Table 4 shows that, at equivalent concentrations, the liquid polyaluminium chloride products obtained in the Examples have lower viscosities and higher basicity than the liquid polyaluminium chloride products obtained in the Comparative Examples. Furthermore, it can be seen that due to the lower viscosity, the liquid polyaluminium chloride products in the Examples are more stable and less likely to form gels. Therefore, before spray drying, the concentration of the liquid polyaluminium chloride products (expressed as Al2O3 content) can exceed 21%. A higher concentration means less water evaporates during the drying process to obtain a solid product, resulting in greater energy savings.

[0108] Test Example 5

[0109] The other main components in the liquid polyaluminium chloride products obtained in the above examples and comparative examples were sent to a testing agency for analysis. The results are shown in Table 5 below.

[0110] Table 5 Other main components in liquid polyaluminium chloride products

[0111] Table 5 shows that the iron and heavy metal contents in the liquid polyaluminum chloride product obtained in the example are far lower than the levels specified in the Chinese national standard GB15892-2020 "Polyaluminum Chloride for Drinking Water".

Claims

1. A method for preparing a polyaluminium chloride product, characterized in that The following steps are involved: a) providing a PAC-containing liquid raw material; b) adding calcium aluminate substantially free of SiO2 to the PAC-containing liquid feedstock; c) optionally filtering to obtain a liquid polyaluminium chloride product.

2. The method of claim 1, wherein: In step a), the PAC-containing liquid raw material contains 10 wt%-20 wt% of Al2O3, preferably 15-19 wt% of Al2O3, and more preferably 17.3-18.3 wt% of Al2O3.

3. The method according to claim 1 or 2, wherein: In step a), the basicity of the PAC-containing liquid raw material is 30-50%, preferably 37-48%, more preferably 41-45%.

4. A method as claimed in any preceding claim, wherein: In step b), the substantially SiO2-free calcium aluminate contains less than or equal to 1 wt% SiO2, preferably less than or equal to 0.3 wt% SiO2, further preferably less than or equal to 0.2 wt% SiO2, more preferably less than or equal to 0.02 wt% SiO2, and most preferably less than or equal to 0.01 wt% SiO2.

5. A method as claimed in any preceding claim, wherein: In step b), the substantially SiO2-free calcium aluminate contains greater than or equal to 60 wt% Al2O3, preferably 60-75 wt% Al2O3.

6. A method as claimed in any preceding claim, wherein: In step b), the calcium aluminate substantially free of SiO2 contains 25-35 wt% CaO, preferably 27-31 wt% CaO.

7. A method as claimed in any preceding claim, wherein: In step b), the substantially SiO2-free calcium aluminate contains less than or equal to 0.2 wt% Fe2O3, preferably less than or equal to 0.1 wt% Fe2O3, and more preferably less than or equal to 0.01 wt% Fe2O3.

8. A method as claimed in any preceding claim, wherein: In step b), the calcium aluminate substantially free of SiO2 is added in the form of powder or slurry, preferably 40-80 wt% slurry.

9. A method as claimed in any preceding claim, wherein: In step b), the calcium aluminate substantially free of SiO2 is calcium aluminate cement, preferably high calcium aluminate cement, more preferably pure calcium aluminate cement.

10. A method as claimed in any preceding claim, wherein: In step c), the basicity of the liquid polyaluminium chloride product is 60-90%, preferably 65-85%.

11. A method as claimed in any preceding claim, wherein: In step c), the liquid polyaluminium chloride product contains greater than or equal to 10 wt% Al2O3, preferably 10-22 wt% Al2O3, more preferably 20-22 wt% Al2O3.

12. A method as claimed in any preceding claim, wherein: In step c), the liquid polyaluminium chloride product contains 10-22 wt% of Al2O3 and has a basicity of 65-85%.

13. A method as claimed in any preceding claim, wherein: In step a), the PAC-containing liquid raw material is prepared using a raw material substantially free of SiO2.

14. A method as claimed in any preceding claim, wherein: In step a), the PAC-containing liquid raw material is prepared using raw materials comprising aluminum hydroxide and hydrochloric acid.

15. A polyaluminium chloride product prepared according to the process of any one of the preceding claims.

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