Method for preparing polyaluminum chloride product for drinking water treatment

Abstract

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

Description

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 widely used in the field of water treatment. After being applied to the water to be treated, PAC forms a polynuclear hydroxyaluminum complex, which flocculates insoluble particles in the water by, for example, electrical neutralization. Alumina (Al2O3) content and basicity (also known as alkalinity) are important indicators of PAC products. High alumina content or high basicity is desirable.

[0003] PAC is usually produced by a one-step process and a two-step process. The one-step process includes a step of contacting an aluminum-containing material (e.g., calcium aluminate, bauxite, aluminum chips, aluminum ash, and aluminum slag) with an acid (e.g., hydrochloric acid). The problem with the one-step process is that it is difficult to obtain high-quality (i.e., drinking water treatment grade) PAC. The two-step process includes a first step of contacting the aluminum-containing material with an acid and then a second step of adding additional alkali (e.g., NaCO3, NaOH, etc.) to increase the basicity.

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

[0005] To obtain a product with a high alumina content, the problem of high viscosity of the reaction system caused by the presence of a large amount of aluminum (i.e., high aluminum concentration) must be solved during the preparation process. To overcome this high viscosity, acid needs to be added, but the addition of acid hinders the realization of high basicity. Similarly, to obtain a product with a high basicity, the amount of acid added needs to be controlled, which ultimately leads to a low alumina content. How to simultaneously increase the basicity and concentration of polyaluminium chloride products is a problem that those skilled in the art have been seeking to solve. Summary of the invention

[0006] The 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.

[0007] In one embodiment, the method of the present invention comprises the following steps:

[0008] a) providing a PAC-containing liquid raw material;

[0009] b) adding calcium aluminate substantially free of SiO2 to the PAC-containing liquid feedstock;

[0010] c) optionally filtering to obtain a liquid polyaluminium chloride product.

[0011] In one embodiment, the method of the present invention further comprises step d):

[0012] The obtained liquid polyaluminium chloride product is dried to obtain a solid polyaluminium chloride product. In a preferred embodiment, the drying is spray drying.

[0013] In one embodiment, in step a), the PAC-containing liquid raw material is prepared using a raw material that is substantially free of SiO2.

[0014] In one embodiment, in step a), the PAC-containing liquid raw material is prepared using raw materials comprising aluminum hydroxide and hydrochloric acid.

[0015] In one embodiment, in step a), the PAC-containing liquid raw material comprises 10 wt%-20 wt% Al2O3. In a preferred embodiment, in step a), the PAC-containing liquid raw material comprises 10 wt%-20 wt% 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, 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, 13.1 .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.

[0016] In one embodiment, in step a), the basicity of the PAC-containing liquid raw material 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 in these ranges.

[0017] In one embodiment, step a) further comprises diluting the provided PAC-containing liquid raw material under optional stirring and / or optional heating conditions. In a preferred embodiment, the stirring rate is 100-10000 rpm, such as 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, 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 values ​​in these ranges.

[0018] In one embodiment, step b) is also carried out under stirring. In a preferred embodiment, the stirring rate is 100-10000rpm, such as 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000rpm, 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, such as 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.

[0019] 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 wt%, less than or equal to 0.09wt%, less than or equal to 0.08wt%, less than or equal to 0.07wt%, less than or equal to 0.06wt%, less than or equal to 0.05wt%, less than or equal to 0.04wt%, less than or equal to 0.03wt%, less than or equal to 0.02wt%, less than or equal to 0.01wt%, less than or equal to 0.009wt%, less than or equal to 0.008wt%, less than or equal to 0.007wt%, less than or equal to 0.006wt%, less than or equal to 0.005wt%, less than or equal to 0.004wt%, less than or equal to 0.003wt%, less than or equal to 0.002wt%, less than or equal to 0.001wt%, or a sub-range consisting of any values ​​in these ranges.

[0020] In one embodiment, the substantially SiO2-free calcium aluminate comprises greater than or equal to 60 wt% Al2O3, e.g., 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 sub-range consisting of any value within these ranges.

[0021] 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.

[0022] 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 a sub-range consisting of any value within these ranges.

[0023] 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.

[0024] In one embodiment, the calcium aluminate substantially free of SiO2 described herein is added in the form of a powder. In another embodiment, the calcium aluminate substantially free of SiO2 described herein is added in the form of a slurry, such as a 40-80 wt% slurry, preferably a 50 wt% slurry.

[0025] 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, 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 in these ranges.

[0026] In a preferred embodiment, in step c), filter paper is used for filtration, preferably glass fiber filter paper, such as the one with catalog number 1820-125. GF / A glass fiber filter paper.

[0027] In a preferred embodiment, in step c), filtering is performed using a filter press, for example, a plate and frame filter press.

[0028] 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, 0, 87.0, 87.5, 88.0, 88.5, 89.0, 89.5, 90.0, 91.0, 92.0, 93.0, 94.5, 95.0, 96.0, 97.0, 98.5, 99.0, 99.5, 100.0, 101.0, 102.0, 103.5, 104.0, 105.5, 106.0, 107.5, 108.0, 109.5, 110.0, 111.5, 112.0, 113.5, 114.0, 115.5, 116.0, 117.5, 118.0, 119.5, 120.0, 121.5, 122.0, 123.5, 124.0, 125

[0029] 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 wt %, or a sub-range consisting of any value within these ranges.

[0030] In a preferred embodiment, the liquid polyaluminium chloride product contains 10-22 wt% Al2O3 and has 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 in these ranges) of Al2O3, and the basicity is 65-85%, for example, 65, 65.1, 65.2, 65.3, 65.4, 65.5, 65.6, 65.7, 65.8, 65.9, 66, 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, 67.7, 67.8, 67.9, 68.10, 68. .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, 7 6.4, 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 sub-range consisting of any value within these ranges. .

[0031] In one embodiment, the liquid polyaluminum chloride product contains less than or equal to 0.05 wt% Si, for example, 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 in these ranges.

[0032] In one embodiment, the liquid polyaluminum chloride product contains less than or equal to 100 ppm Fe, for example, 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 in these ranges.

[0033] The method of the present invention is very simple, 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 concentrations of Al2O3 (e.g., Al2O3>20%) and / or high basicity. The PAC product prepared by the method of the present invention has high stability and does not require the addition of stabilizers. The PAC product prepared by the method of the present invention can be used for drinking water treatment. After treatment with the PAC product prepared by the method of the present invention, the residual aluminum in the treated water is much lower than the reference value.

[0034] Unless otherwise specified, the percentages, proportions, ratios, contents or parts described herein are by weight.

[0035] The term "substantially free of" used in the present invention means that the content is less than 1% (by weight) or a specified amount.

[0036] The "room temperature" mentioned in the present invention refers to a temperature of 10-35°C, preferably 20-25°C.

[0037] The "polyaluminium chloride product" of the present invention can be provided in liquid or solid form.

[0038] In the present invention, the concentration (i.e., Al2O3wt%) and basicity of the polyaluminium chloride product are measured according to the general method 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

[0039] In order to better understand the present invention, the content of the present invention is further described below in conjunction with the examples, but the content of the present invention is not limited to the following examples. The experimental operations described in the following examples are conventional operations unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0040] Example 1

[0041] Preparation of 1kg high basicity polyaluminium chloride product:

[0042] a) taking 364.9 g of PAC-containing liquid raw material (PAX 10, which is a medium-basicity PAC available on the market, produced by the reaction of Al(OH)3 and HCl. It contains 10 wt% Al2O3 and has a basicity of 40%; the source and composition of the raw material in the following Examples 2-3 and Comparative Examples 1-3 are exactly the same as those in Example 1); adding 569.9 g of water to the PAC-containing liquid raw material, stirring at 260 rpm; heating to 90° C., stirring continuously;

[0043] b) adding 65.2 g of calcium aluminate substantially free of SiO2 (a commercially available product containing 0.21 wt% SiO2, 68.9 wt% Al2O3, 27.7 wt% CaO and 0.12 wt% Fe2O3; the source and composition of the raw materials in the following Examples 2-3 are exactly the same as 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;

[0044] c) By The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0045] After analysis, the obtained liquid polyaluminium chloride product contained 10.0wt% Al2O3 and the basicity was 76.3%.

[0046] Example 2

[0047] Preparation of 1kg high-concentration, high-basicity polyaluminium chloride product for drinking water treatment:

[0048] a) taking 610.6 g of PAC-containing liquid raw material; adding 272.4 g of water to the PAC-containing liquid raw material, stirring at 260 rpm; heating to 90° C., and continuously stirring;

[0049] 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; cooling the solution to room temperature;

[0050] c) By The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0051] The obtained liquid polyaluminium chloride product was analyzed to contain 18.4 wt% Al2O3 and a basicity of 75%.

[0052] Example 3

[0053] Preparation of 1kg of extremely high concentration, high basicity polyaluminium chloride product for drinking water treatment:

[0054] a) taking 678.4 g of 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 continuously stirring;

[0055] 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; cooling the solution to room temperature;

[0056] c) By The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0057] The obtained liquid polyaluminium chloride product was analyzed to contain 21.7 wt% Al2O3 and a basicity of 70.3%.

[0058] Comparative Example 1

[0059] Preparation of 1kg high basicity polyaluminium chloride product for drinking water treatment:

[0060] 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;

[0061] b) adding 68.5 g of calcium aluminate powder for ordinary water treatment (which is a product obtained on the market, containing 7.1 wt% SiO2, 54.7 wt% Al2O3, 31.6 wt% CaO and 1.6 wt% Fe2O3; the source and composition of the raw materials in the following Comparative Examples 2-3 are exactly the same as 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;

[0062] c) By The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0063] After analysis, the obtained liquid polyaluminium chloride product contained 10.5wt% Al2O3 and the basicity was 70.2%.

[0064] Comparative Example 2

[0065] Preparation of 1kg high-concentration, high-basicity polyaluminium chloride product for drinking water treatment:

[0066] a) taking 648.4 g of 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 continuously stirring;

[0067] 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;

[0068] c) By The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0069] The obtained liquid polyaluminium chloride product was analyzed to contain 18.7 wt% Al2O3 and a basicity of 69.4%.

[0070] Comparative Example 3

[0071] Preparation of 1kg of extremely high concentration, high basicity polyaluminium chloride product for drinking water treatment:

[0072] 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 continuously stirring;

[0073] 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;

[0074] c) By The solution is filtered through a GF / A filter to obtain a liquid polyaluminium chloride product.

[0075] After analysis, the obtained liquid polyaluminium chloride product contained 21.8 wt% Al2O3 and the basicity was 69.6%.

[0076] Comparative Example 4

[0077] PAC_2009 is a commercially available high-basicity PAC product, containing 10.9 wt% Al2O3 and a basicity of 66.2%.

[0078] Comparative Example 5

[0079] PAX-HB800, which is a commercially available high basicity PAC, is produced by adding sodium carbonate to medium basicity PAC. It does not contain a stabilizer, so the stability of the sample is affected (short shelf life). It contains 11.1 wt% Al2O3 and has a basicity of 69.1%.

[0080] Comparative Example 6

[0081] PAX-HB9, which is a commercially available high-basicity PAC, is produced by adding sodium carbonate to medium-basicity PAC. It also contains some divalent anions, which can enhance performance during application. However, it does not contain stabilizers. It contains 9.1wt% Al2O3 and has a basicity of 70.7%.

[0082] Comparative Example 7

[0083] PAX-HB10, which is a commercially available high basicity PAC, is produced by adding sodium carbonate to medium basicity PAC. It also contains some divalent anions to enhance performance during application. It also contains some stabilizers to improve product stability. It contains 10.1wt% Al2O3 and has a basicity of 76.8%.

[0084] Comparative Example 8

[0085] PAX-HB1, which is 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%.

[0086] Comparative Example 9

[0087] 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%.

[0088] 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.

[0089] Test Example 1

[0090] The liquid polyaluminium chloride products obtained in the above examples and comparative examples were stored at 50°C, and the stability of the products was monitored by visual observation, specifically by visually observing whether precipitation was formed and recording the elapsed time. The results are shown in Table 1 below.

[0091] Table 1 Stability of liquid polyaluminium chloride products

[0092]

[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 GB5749-2022 Drinking Water Hygiene Standard). Aluminum is present 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 of a drinking water treatment plant, wherein 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]

[0099]

[0100] 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.

[0101] Test Example 3

[0102] There is a close correlation between the concentration of dissolved organic carbon (DOC) in natural water and the ultraviolet absorbance at 254nm (UVA 254nm). Therefore, UVA 254nm is often used as a general indicator of organic load 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).

[0103] The liquid polyaluminium chloride product obtained in the above embodiment and comparative example was used to treat the reservoir water of the drinking water treatment plant. The ultraviolet absorbance of the water before treatment at 254nm was 0.087. The results are shown in Table 3 below.

[0104] Table 3 UV absorbance of treated water at 254 nm

[0105]

[0106]

[0107]

[0108] 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.

[0109] Test Example 4

[0110] The viscosity of the liquid polyaluminium 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 is dynamic viscosity, and the instrument used is a rotational viscometer (model: LVDV-1 Prime, manufacturer: Brookfield).

[0111] Table 4 Viscosity of liquid polyaluminium chloride products

[0112]

[0113] Table 4 shows that, at the same concentration, the viscosity of the liquid polyaluminium chloride product obtained in the embodiment is lower than that of the liquid polyaluminium chloride product obtained in the comparative example, and the basicity is higher. It can also be seen that due to the lower viscosity, the system of the liquid polyaluminium chloride product in the embodiment is more stable and not easy to form a gel. Therefore, before spray drying, the concentration of the liquid polyaluminium chloride product (expressed as Al2O3 content) can exceed 21%. A higher concentration means that less water evaporates when a solid product is obtained during the drying process, which is more energy-efficient.

[0114] Test Example 5

[0115] 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.

[0116] Table 5 Other main components in liquid polyaluminium chloride products

[0117]

[0118] Table 5 shows that the iron and heavy metal contents in the liquid polyaluminium chloride product obtained in the example are far lower than the levels specified in the Chinese national standard GB15892-2020 "Polyaluminium 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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