Softening treatment method for high-calcium and high-sulfate-radical sewage

Abstract

The invention discloses a softening treatment method for high-calcium and high-sulfate radical sewage. By adding the seed crystal, calcium sulfate is crystallized to achieve the purpose of removing calcium ions, so that the generation of chemical sludge is avoided, and the cost of treating the chemical sludge is further reduced; according to the invention, the seed crystal is selected according to the saturation degree of the sewage, and the dosage of the seed crystal is determined, so that the selection of the optimal seed crystal type and dosage is achieved, the cost is saved, and the purpose of softening water is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of high-calcium and high-sulfate sewage treatment, and in particular to a softening treatment method for high-calcium and high-sulfate sewage. Background Art

[0002] At present, for sewage with high calcium and high sulfate characteristics, the industry mainly uses traditional chemical methods to soften high-hardness sewage. By adding sodium hydroxide, sodium bicarbonate and other reagents, the calcium ions in the sewage react with carbonate ions to form calcium carbonate precipitates. However, the main problem with this method is that the generated calcium carbonate precipitates will eventually form chemical sludge with high water content, which is difficult to handle and cannot be recycled. At the same time, the cost of reagents such as sodium hydroxide and sodium bicarbonate is expensive, and the cost of sewage softening per ton of water is too high. Therefore, taking advantage of the high calcium and high sulfate characteristics of sewage, removing calcium ions in water by calcium sulfate crystallization is the main direction of exploring economic sewage softening methods. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

[0004] To this end, an embodiment of the present invention provides a method for softening high-calcium and high-sulfate wastewater.

[0005] The present invention provides a method for softening high-calcium and high-sulfate sewage, comprising the following steps:

[0006] (a) Determine the saturation level of sewage;

[0007] (b) selecting crystal seeds according to the saturation degree of the sewage;

[0008] (c) Design a gradient test to determine the amount of seed crystals to be added.

[0009] Furthermore, in the step (a), the ionic activity product IAP of calcium sulfate dihydrate crystals and the thermodynamic solubility product constant K sp θ The relative size of the wastewater determines the saturation degree of the wastewater, and the wastewater is divided into unsaturated solution, saturated solution and supersaturated solution according to the saturation degree.

[0010] Further, the dynamic equilibrium process of calcium sulfate dihydrate crystallization and dissolution is shown in the following formula:

[0011]

[0012] The ion activity product of the calcium sulfate dihydrate crystals in, is the activity of calcium ions in the solution, is the activity of sulfate ions in the solution, α wis the activity of water molecules in the solution.

[0013] Furthermore, when IAP <K sp θ When IAP=K sp θ When IAP>K sp θ When , the sewage is a supersaturated solution.

[0014] Furthermore, the step (b) comprises:

[0015] The solubility characteristics of crystal seeds in sewage with different saturation levels were tested, and crystal seeds that did not dissolve in the corresponding water quality were selected.

[0016] Furthermore, when the sewage is an unsaturated solution, the seed crystals include one of garnet crystal particles, quartz sand crystal particles, activated carbon particles, and boron crystal particles.

[0017] Furthermore, when the sewage is a saturated solution or a supersaturated solution, the seed crystals include one of industrial-grade gypsum crystal powder, calcium sulfate whiskers, calcium carbonate crystal particles, calcium fluoride crystal particles, and calcium silicate crystal particles.

[0018] Furthermore, the step (c) comprises: carrying out a gradient test while keeping the amount of seed crystal added as the only variable, and determining the calcium ion concentration in the treated effluent water quality.

[0019] Furthermore, the optimal seed dosage is when the removal rate of calcium ions in the sewage reaches more than 25%.

[0020] Furthermore, the method also includes softening the sewage according to the type of the selected crystal seeds and the amount of the crystal seeds added.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] The invention achieves the purpose of removing calcium ions by adding crystal seeds to make calcium sulfate crystals, thereby avoiding the generation of chemical sludge and reducing the cost of treating the chemical sludge. The invention selects crystal seeds and determines the addition amount of the crystal seeds according to the saturation degree of sewage, achieves the selection of the optimal crystal seed type and addition amount, saves costs, and achieves the purpose of softening water quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0024] Figure 1 The present invention is a flow chart of the softening treatment method of high-calcium and high-sulfate sewage;

[0025] Figure 2 This is a bar graph of the quality of the gypsum crystal powder and garnet crystal particles after filtration and drying in water quality 1 and water quality 2 of the present invention;

[0026] Figure 3 This is a data diagram of ion concentration in water quality 1 under different garnet crystal particle dosage conditions of the present invention;

[0027] Figure 4 This is a graph showing the ion concentration data of water quality 2 under different gypsum crystal powder addition conditions of the present invention. DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0029] The softening treatment method for high-calcium and high-sulfate wastewater proposed by the present invention is described below in conjunction with the accompanying drawings.

[0030] like Figure 1 As shown, the softening treatment method of high-calcium and high-sulfate sewage of the present invention comprises the following steps:

[0031] (a) Determine the saturation level of sewage;

[0032] (b) selecting crystal seeds according to the saturation degree of the sewage;

[0033] (c) designing a gradient test to determine the amount of seed crystal to be added;

[0034] (d) Softening the sewage according to the type of seed crystals selected and the amount of seed crystals added.

[0035] Wherein, in step (a), the high calcium and high sulfate wastewater is divided into unsaturated solution, saturated solution and supersaturated solution according to the degree of saturation. According to the ionic activity product IAP of calcium sulfate dihydrate crystals and the thermodynamic solubility product constant K sp θ The relative size determines the degree of saturation of the sewage.

[0036] When calcium sulfate in water crystallizes, it mostly undergoes a crystallization reaction in the form of calcium sulfate dihydrate. The reaction process mainly exists as shown in formula (1-1). There is a dynamic equilibrium process of calcium sulfate dihydrate crystallization and dissolution in water.

[0037]

[0038] The ion activity product of calcium sulfate dihydrate crystals is shown in formula (1-2): in, is the activity of calcium ions in the solution, is the activity of sulfate ions in the solution, α W is the activity of water molecules in the solution.

[0039] K sp θ It is the thermodynamic solubility product constant, which is only related to temperature. SI represents the saturated state of a substance in water. SI, IAP and K sp θ The relationship can be calculated by the following formula (1-3): SI = log IAP - log K sp θ (1-3).

[0040] According to the crystallization thermodynamics principle, the Gibbs free energy change ΔG can be expressed by the supersaturation index SI:

[0041]

[0042] In the calcium sulfate dihydrate crystallization system, the relationship between the ion activity product and the solubility product, that is, the size of the supersaturation index, affects the dynamic equilibrium relationship between crystallization and dissolution, which is specifically manifested as follows:

[0043] When IAP=K sp θ When SI = 0, ΔG = 0, it means it is a saturated solution, and the crystallization and dissolution in the solution reach a dynamic equilibrium;

[0044] When IAP<K sp θ When SI < 0, ΔG > 0, it indicates an unsaturated solution, and no crystals precipitate from the solution;

[0045] When IAP>K sp θ When SI>0 and ΔG<0, it indicates a supersaturated solution, and crystallization reaction will occur in the solution.

[0046] Step (b) includes testing the solubility characteristics of the crystal seeds in sewage with different saturation levels, and selecting the crystal seeds that do not dissolve in the corresponding water quality.

[0047] In the process of induced crystallization, the induction carrier has an important influence on the reaction process. Usually, the crystals of the induced crystallization product or the crystals with the same crystal form or stereo configuration as the crystallized product are used as induction seeds. In practical applications, factors such as the sedimentation performance, density, and physical and chemical properties of the seeds also need to be considered. The selection of the induction seed type has a direct impact on the crystallization effect. The general principles for the selection of induction seeds in the chemical crystallization method are: strong induction ability, strong sedimentation performance, good fluidity, stable properties, good strength, and cheap and easy to obtain.

[0048] When the sewage is an unsaturated solution, the seed crystals include one of garnet crystal particles, quartz sand crystal particles, activated carbon particles, and boron crystal particles.

[0049] When the sewage is a saturated solution or a supersaturated solution, the seed crystals include one of industrial-grade gypsum crystal powder, calcium sulfate whiskers, calcium carbonate crystal particles, calcium fluoride crystal particles, and calcium silicate crystal particles.

[0050] Step (c) comprises: carrying out a gradient test while keeping the amount of seed crystal added as the only variable, determining the calcium ion concentration in the treated effluent water quality, and the seed crystal addition amount when the calcium ion removal rate in the sewage reaches more than 25% is the optimal addition amount.

[0051] The method of the present invention is described below with reference to specific embodiments.

[0052] Two types of water quality were selected, namely, water quality 1 in which calcium sulfate was in an unsaturated state and water quality 2 in which calcium sulfate was in an oversaturated state. The detailed indicators of water quality 1 and water quality 2 are shown in Table 1 below.

[0053] Table 1:

[0054] Serial number pH <![CDATA[HCO3 - / mM]]> <![CDATA[CO3 2- / mM]]> Total hardness / mM <![CDATA[Ca 2+ / mM]]> <![CDATA[SO4 2- / mM]]> 1 7.81 1 0.15 4.2 2.02 78.8 2 6.38 0.75 0.75 25.84 25.4 49.77

[0055] Industrial-grade gypsum crystal powder and garnet crystal particles were selected as induced crystal seeds for the test. First, the solubility characteristics of the two crystal seeds in the two raw waters need to be tested to ensure the reliability of the static test results. In the crystal seed solubility test, 5g of crystal seeds were weighed and added to 1L of raw water. After sufficient stirring, the reaction solution was filtered using a 0.45μm filter membrane. The filtered material was dried and the mass was measured. The mass of the dried crystal seeds is as follows: Figure 2 shown.

[0056] according to Figure 2The results of the seed solubility test show that the mass of garnet crystal particles after filtering and drying in water quality 1 and water quality 2 is 5g, that is, garnet crystal particles will not dissolve in both water qualities; the mass of gypsum crystals after filtering and drying in water quality 1 is 2.25g, and gypsum crystal powder will dissolve to a certain extent in water quality 1; the mass of gypsum crystals after filtering and drying in water quality 2 is 5g, and gypsum crystal powder does not dissolve in water quality 2, which is related to the CaSO4 saturation state of the raw water. In order to ensure the accuracy and reliability of static test data, garnet crystal particles were selected as induced seeds in the water quality 1 test, and industrial-grade gypsum crystal powder was selected as induced seeds in the water quality 2 test.

[0057] According to the mechanism of induced crystallization, the amount of induced crystal seeds is an important factor affecting the crystallization effect. Under room temperature, different amounts of induced crystal seeds were added for two raw water qualities. Other control conditions remained the same and the effluent quality was measured. The test results are as follows: Figure 3 shown.

[0058] Among them, the test process for water quality 1 is: the design of seed crystal dosage is 0g / L, 10g / L, 20g / L, 30g / L, 40g / L, 50g / L, 60g / L, add the seed crystal to the raw water, stir well to complete the reaction, and then test the concentrations of calcium ions, bicarbonate ions, and sulfate ions in the treated water. The test process for water quality 2 is: the design of seed crystal dosage is 0g / L, 40g / L, 50g / L, 60g / L, 70g / L, 80g / L, 90g / L, 100g / L, add the seed crystal to the raw water, stir well to complete the reaction, and then test the concentrations of calcium ions, bicarbonate ions, and sulfate ions in the treated water.

[0059] according to Figure 3 It can be seen that induced crystallization technology can effectively reduce the hardness and SO4 in water 2- Content, increasing the amount of seed crystals added has an improved effect on the crystallization effect of CaSO4 in both raw waters. In the process of induced crystallization, the addition of seed crystals can induce the formation of crystal nuclei, which can reduce the potential barrier for the formation of crystal nuclei to a certain extent, thereby promoting the occurrence of the crystallization process. In addition, the seed crystals also provide a larger contact area for the aggregation of crystals, which also has a positive effect on the crystallization process. For water quality 1, when the seed crystal dosage is 40g / L, continuing to increase the seed crystal dosage does not significantly improve the softening effect. Therefore, the seed crystal dosage of 40g / L is selected as the optimal dosage for unsaturated water quality. Similarly, for water quality 2, 80g / L is selected as the optimal dosage for supersaturated water quality.

[0060] According to the above, for water quality 1, garnet crystal particles are used as induced crystal seeds, and the water quality 1 is softened at a dosage of 40g / L; for water quality 2, industrial-grade gypsum crystal powder is used as induced crystal seeds, and the water quality 2 is softened at a dosage of 80g / L.

[0061] The invention achieves the purpose of removing calcium ions by adding crystal seeds to make calcium sulfate crystals, thereby avoiding the generation of chemical sludge and reducing the cost of treating the chemical sludge. The invention selects crystal seeds and determines the addition amount of the crystal seeds according to the saturation degree of sewage, achieves the selection of the optimal crystal seed type and addition amount, saves costs, and achieves the purpose of softening water quality.

[0062] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms may be for different embodiments or examples. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0063] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0064] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for softening high-calcium and high-sulfate sewage, characterized in that: The following steps are involved: (a) Determine the saturation level of sewage; (b) selecting crystal seeds according to the saturation degree of the sewage; (c) Design a gradient test to determine the amount of seed crystals to be added.

2. The method according to claim 1, characterized in that In the step (a), the ionic activity product IAP of calcium sulfate dihydrate crystals and the thermodynamic solubility product constant K sp θ The relative size of the wastewater determines the saturation degree of the wastewater, and the wastewater is divided into unsaturated solution, saturated solution and supersaturated solution according to the saturation degree.

3. The method according to claim 2, characterized in that The dynamic equilibrium process of calcium sulfate dihydrate crystallization and dissolution is shown in the following formula: The ion activity product of the calcium sulfate dihydrate crystals in, is the activity of calcium ions in the solution, is the activity of sulfate ions in the solution, α w is the activity of water molecules in the solution.

4. The method according to claim 3, characterized in that When IAP <K sp θ When IAP=K sp θ When IAP>K sp θ When , the sewage is a supersaturated solution.

5. The method according to claim 1, characterized in that The step (b) comprises: The solubility characteristics of crystal seeds in sewage with different saturation levels were tested, and crystal seeds that did not dissolve in the corresponding water quality were selected.

6. The method according to claim 5, characterized in that When the sewage is an unsaturated solution, the seed crystals include one of garnet crystal particles, quartz sand crystal particles, activated carbon particles, and boron crystal particles.

7. The method according to claim 5, characterized in that When the sewage is a saturated solution or a supersaturated solution, the seed crystals include one of industrial-grade gypsum crystal powder, calcium sulfate whiskers, calcium carbonate crystal particles, calcium fluoride crystal particles, and calcium silicate crystal particles.

8. The method according to claim 1, characterized in that The step (c) comprises: carrying out a gradient test while keeping the amount of seed crystal added as the only variable, and measuring the calcium ion concentration in the treated effluent water quality.

9. The method according to claim 8, characterized in that The optimal dosage of the seed crystals is when the removal rate of calcium ions in the sewage reaches more than 25%.

10. The method according to claim 1, characterized in that The method also includes softening the sewage according to the type of the selected crystal seeds and the amount of the crystal seeds added.

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