Kinetic prediction method for induced crystallization of calcium sulfate in wastewater

Abstract

The invention belongs to the field of wastewater treatment and crystallization kinetics, and provides a kinetics prediction method for induced crystallization of calcium sulfate in wastewater, which comprises the following steps: detecting to obtain a water quality index, and calculating the solution supersaturation degree S and the initial chemical potential driving force delta mu through the water quality index; calculating values of a first saturation parameter a, a second saturation parameter b and a third saturation parameter c according to the saturation S; according to the parameters a, b and c and the chemical potential driving force delta mu, calcium ion concentration values at different crystallization moments are calculated, and the progress of removing Ca < 2 + > in the wastewater is determined. According to the method, the ion concentration change value under each crystallization reaction condition can be calculated, the accurate regulation and control of the calcium sulfate crystallization process are realized, and a theoretical support is provided for the industrial process control of calcium sulfate induced crystallization.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment and crystallization kinetics, and particularly relates to a method for predicting calcium sulfate-induced crystallization kinetics in wastewater. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The treatment of high-salinity wastewater and desulfurization wastewater is a huge challenge in achieving zero discharge of industrial wastewater. The former mainly comes from seawater concentration and desalination, industrial brine discharge and wastewater reuse, while the latter is the most difficult type of wastewater to treat in coal-fired power plants. The ions contained in these two types of wastewater are mainly Na + , K + , Ca 2+ Mg 2+ , Cl - 、SO4 2- Due to its high hardness and high salt content, scaling is very likely to occur when treating such wastewater. In order to avoid equipment damage and thus economic losses, the scaling factors are often controlled at a low level in advance by pre-treating the raw water.

[0004] Using the induced crystallization method to remove calcium sulfate from saline wastewater in advance can significantly increase the hardness removal rate and reduce the cost of softening agent addition. Induced crystallization strengthens the crystallization process by adding crystal seeds, and the thermodynamic driving force promotes the Ca in the solution to 2+ and SO4 2- Mass transfer is constantly taking place at the solid-liquid interface. Since the energy required for the dissolved ions to react with existing crystals is much lower than the energy required to produce new crystals, especially when the seed dosage is high, the induced crystallization reaction occurs very quickly, making it difficult to capture its kinetic changes. In addition, in the actual wastewater treatment process, water quality indicators often fluctuate within a certain range. In order to cope with the adjustment of on-site process parameters, a large number of experiments are required to accumulate calcium sulfate crystallization kinetic data, which is time-consuming and labor-intensive, and the accuracy is relatively poor. Summary of the invention

[0005] The purpose of the present invention is to provide a method for predicting the kinetics of calcium sulfate-induced crystallization in wastewater, so as to solve the technical problem that the crystallization kinetics data in the prior art need to be accumulated through a large number of experiments.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for predicting the kinetics of calcium sulfate induced crystallization in wastewater, comprising the following steps:

[0007] Step 1: Obtain water quality indicators, and calculate the solution supersaturation S and initial chemical potential driving force Δμ0 through the water quality indicators;

[0008] Step 2: Calculate the values ​​of parameters a, b, and c based on supersaturation;

[0009] Step 3: According to the parameters a, b, c and the initial chemical potential driving force Δμ0, the calcium ion concentration values ​​at different crystallization times are calculated using the following formula:

[0010]

[0011] Where V represents the volume of the solution and c1 represents Ca 2+ concentration, T represents the thermodynamic temperature during crystallization, R represents the ideal gas constant, and Δμ represents the chemical potential driving force;

[0012] Step 4: Based on the calculation results of step 3, determine the Ca content in the wastewater. 2+ The progress being removed.

[0013] The supersaturation S value is between 1.2 and 8.5.

[0014] In step 2, the calculation formulas of parameters a, b, and c are:

[0015] a=0.0021S 2 +0.00504S - 0.00154;

[0016] b=―0.17504S 2 +1.4570S-1.77625;

[0017] c=0.02861S 2 +0.1046S+0.19947;

[0018] Here, S represents the supersaturation of the solution.

[0019] In step 1, the calculation formula of the solution supersaturation S is:

[0020]

[0021] Among them, IAP and K sp They represent the ion product and solubility product constants of calcium sulfate dihydrate in solution respectively.

[0022] In step 1, the calculation formula of the initial chemical potential driving force Δμ0 is:

[0023]

[0024] in, and Respectively represent Ca 2+ and SO4 2- The ion activity in the bulk solution, and Respectively represent Ca 2 + and SO4 2- The activity of ions in a saturated solution.

[0025] In the step 1, water quality indicators are obtained through testing.

[0026] In step 1, the water quality indicators detected include: the ion product and solubility product constant of calcium sulfate dihydrate in the solution, Ca 2+ and SO4 2- The ion activity in the bulk solution, Ca 2+ and SO4 2- The activity of ions in a saturated solution.

[0027] In step 3, the expression of the chemical potential driving force is:

[0028]

[0029] in, and Ca 2+ and SO4 2- The ionic activity coefficients of c1 and c2 represent the Ca 2+ and SO4 2- The concentration of and Respectively represent Ca 2+ and SO4 2- The activity of ions in a saturated solution.

[0030] In step 3, Ca 2+ and SO4 2- The ion activity coefficient calculation formula is:

[0031]

[0032] Among them, z1 and z2 represent Ca 2+ and SO4 2- The ionic charge concentrations of α1 and β1 are Ca 2+ The first and second parameters, α2 and β2, are SO4 2- The first and second parameters of , A and B are the first and second coefficients respectively, and I is a constant related to the ion charge concentration in the solution, and its expression is:

[0033] A=1.82×10 6 (εT) ―3 / 2 ;

[0034] B=50.3(εT) ―1 / 2 ;

[0035]

[0036] ε is the dielectric constant of water, c i is the ion concentration in the solution, z i is the charge concentration of each ion in the solution.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The invention provides a method for predicting the kinetics of calcium sulfate-induced crystallization in wastewater, takes supersaturation as the fundamental factor affecting the crystallization kinetics, optimizes the driving force term of the crystallization process through an activity coefficient model, establishes a calculation model for the kinetics of calcium sulfate-induced crystallization, and calculates the change data of solution concentration over time within a certain supersaturation range by measuring the quality of raw water, which can effectively reduce the number of pre-experiments and provide theoretical guidance for the actual crystallization process. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic flow chart of a method for predicting the kinetics of calcium sulfate-induced crystallization in wastewater provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] Example 1

[0042] like Figure 1 As shown, the embodiment of the present invention provides a method for predicting the kinetics of calcium sulfate-induced crystallization in wastewater, taking supersaturation as the fundamental factor affecting the crystallization kinetics, optimizing the driving force term of the crystallization process through the activity coefficient model, and establishing a calculation model for the kinetics of calcium sulfate-induced crystallization. By measuring the quality of the raw water, the change data of the solution concentration over time within a certain supersaturation range can be calculated, which can effectively reduce the number of pre-experiments and provide theoretical guidance for the actual crystallization process. Specifically, the following steps are included:

[0043] Step 1: Detect and obtain water quality indicators, and calculate the solution supersaturation S and initial chemical potential driving force Δμ0 through the water quality indicators.

[0044] In step 1, the water quality indicators detected include: the ion product and solubility product constant of calcium sulfate dihydrate in the solution, Ca 2+ and SO42- Ion activity in bulk solution and Ca 2+ and SO4 2- Ion activity in saturated solution and The solution supersaturation S and the initial chemical potential driving force Δμ0 were calculated using the extended Debye-Hückel model.

[0045] Specifically, in step 1, the calculation formula of the solution supersaturation S is:

[0046]

[0047] Among them, IAP and K sp They represent the ion product and solubility product constants of calcium sulfate dihydrate in solution respectively.

[0048] Specifically, in step 1, the calculation formula of the initial chemical potential driving force Δμ0 is:

[0049]

[0050] in, and Respectively represent Ca 2+ and SO4 2- The ion activity in the bulk solution, and Respectively represent Ca 2+ and SO4 2- The activity of ions in a saturated solution.

[0051] Step 2: Calculate the values ​​of the first saturation parameter a, the second saturation parameter b, and the third saturation parameter c according to the supersaturation;

[0052] Specifically, in step 2, the calculation formulas for parameters a, b, and c are:

[0053] a=0.0021S 2 +0.00504S―0.00154; (3)

[0054] b=―0.17504S 2 +1.4570S-1.77625; (4)

[0055] c=0.02861S 2 +0.1046S+0.19947; (5)

[0056] Here, S represents the supersaturation of the solution.

[0057] Furthermore, in this embodiment, the supersaturation S value is between 1.2 and 8.5.

[0058] Step 3: According to the parameters a, b, c and the chemical potential driving force Δμ, the calcium ion concentration values ​​at different crystallization times are calculated using the following formula:

[0059]

[0060] Where V represents the volume of the solution and c1 represents Ca 2+ concentration, T represents the thermodynamic temperature during crystallization, R represents the ideal gas constant, and Δμ represents the chemical potential driving force. The calculation formula is:

[0061]

[0062] Specifically, in this embodiment, formula (6) is obtained by extending the Debye-Hückel model. According to the extended Debye-Hückel model, the ion activity coefficient of each component in the solution is:

[0063]

[0064] Among them, i = 1, 2, corresponding to Ca 2+ and SO4 2- ; γ B i is the ion activity coefficient of each ion, z i is the charge concentration of each ion in the solution; α i and β i are the first and second parameters of the ion, respectively. For Ca 2+ and SO4 2- , α1=α2=5, for Ca 2+ , β1=0.165, for SO4 2- , β2 = -0.040; A, B are the first coefficient and the second coefficient respectively, I is a constant related to the ionic charge concentration in the solution, and its expression is:

[0065] A=1.82×10 6 (εT) ―3 / 2 ; (9)

[0066] B=50.3(εT) ―1 / 2 ; (10)

[0067]

[0068] Among them, c i is the ion concentration in the solution, and ε is the dielectric constant of water (ε=76.57, 303.15K).

[0069] In addition, the activity of ions and ion concentration have the following relationship:

[0070]

[0071] Then formula (7) can be written as:

[0072]

[0073] in, and Ca 2+ and SO4 2 The ionic activity coefficients of c1 and c2 represent the Ca 2+ and SO4 2 The concentration of and Respectively represent Ca 2+ and SO4 2- The activity of ions in a saturated solution.

[0074] Therefore, by combining formula (6) and formulas (8) to (13), the calcium ion concentration c1 at different crystallization times can be solved. Specifically, by substituting formulas (8) to (11) into formula (13), the expression of the chemical potential driving force Δμ can be obtained, and then the expression of the parameters a, b, c and the chemical potential driving force Δμ is substituted into formula (6), and the equation of formula (6) is solved to obtain the calcium ion concentration c1 at different crystallization times.

[0075] Step 4: Based on the calculation results of step 3, determine the Ca content in the wastewater. 2+ The progress being removed.

[0076] Experimental Example 1

[0077] In this experimental example, the main ion content of the wastewater is: 50mmol / L Ca 2+ 、50mmol / L SO4 2- 、100mmol / LCl - , 100mmol / L Na + According to the above ion content, the calculation of calcium sulfate induced crystallization kinetics data includes the following steps:

[0078] (1) The ion activity coefficients in the solution were calculated according to the extended Debye-Hückel model. Substituting them into equations (1) and (2), the supersaturation S and initial chemical potential driving force Δμ0 at 303.15 K were 4.18 and 1802.486 J / mol, respectively;

[0079] (2) Substituting the supersaturation S into equations (3)-(5), the three parameters a, b, and c are calculated to be 0.0562, 1.256, and 1.137, respectively.

[0080] (3) Substituting the parameters a, b, and c into equation (6), we have:

[0081]

[0082] Combined with the value of the initial chemical potential driving force Δμ0, equations (7) to (13) are used to solve the calcium ion concentration c1 at different crystallization times.

[0083] (4) Solve and experiment to obtain Ca at each time 2+ The concentrations are shown in Table 1:

[0084] time 0s 10s 30s 50s 80s 110s 150s 210s Calculated Value 50.00 38.32 30.97 29.29 28.07 27.36 26.73 26.12 Experimental value 50.00 37.50 33.33 31.17 30.00 27.93 26.73 25.83 time 5min 7min 9min 12min 15min 20min 30min 60min Calculated Value 25.55 25.08 24.78 24.49 24.31 24.14 24.00 23.94 Experimental value 25.03 24.77 24.50 24.23 24.00 23.90 23.90 23.90

[0085] The calculation results show that after 60 minutes, more than 50% of the Ca in the wastewater 2+ was removed, approaching 84% of the thermodynamic limit of calcium sulfate crystallization in this water quality. Correlation between calculated value and experimental value (R 2 ) is 0.99.

[0086] Experimental Example 2

[0087] In this experimental example, the main ion content of the wastewater is: 25mmol / L Ca 2+ 、25mmol / L SO4 2- 、50mmol / LCl - , 50mmol / L Na + According to the above ion content, the calculation of calcium sulfate induced crystallization kinetics data includes the following steps:

[0088] (1) The ion activity coefficients in the solution were calculated according to the extended Debye-Hückel model. Substituting them into equations (1) and (2), the solution supersaturation S and initial chemical potential driving force Δμ0 at 303.15 K were 1.63 and 615.0416 J / mol, respectively;

[0089] (2) Substituting the supersaturation S into equations (3)-(5), the three parameters a, b, and c are calculated to be 0.0123, 0.134, and 0.446, respectively.

[0090] (3) Substituting the parameters a, b, and c into equation (6), we have:

[0091]

[0092] The simultaneous equations (7) to (13) are used to solve the calcium ion concentration c1 at different crystallization times.

[0093] (4) Solve and experiment to obtain Ca at each time 2+ The concentrations are shown in Table 2:

[0094] time 0s 10s 30s 50s 80s 110s 150s 180s Calculated Value 25.00 23.74 22.52 22.26 22.07 21.96 21.87 21.82 Experimental value 25.00 23.75 22.68 22.51 22.34 22.10 22.03 21.99 time 5min 9min 12min 15min 20min 30min 60min Calculated Value 21.69 21.57 21.52 21.50 21.47 21.44 21.43 Experimental value 21.82 21.65 21.48 21.48 21.48 21.48 21.48

[0095] The calculation results show that after 60 minutes, more than 50% of the Ca in the wastewater 2+ was removed, approaching 50% of the thermodynamic limit of calcium sulfate crystallization in this water quality. Correlation between calculated value and experimental value (R 2 ) is 0.995.

[0096] Experimental Example 3

[0097] In this experimental example, a prediction method for calcium sulfate-induced crystallization kinetics of desulfurization wastewater from a steel plant is provided. The desulfurization wastewater is tested for water quality after pretreatment. The main ion content is: 46.4mmol / L Ca 2+ 、1.6mmol / L Mg 2+ 、47.6mmol / L SO4 2- 、150mmol / L Cl - , 60mmol / L Na + According to the above ion content, the calculation of calcium sulfate induced crystallization kinetics data includes the following steps:

[0098] (1) The ion activity coefficients in the solution were calculated according to the extended Debye-Hückel model. Substituting them into equations (1) and (2), the supersaturation of the solution and the initial chemical potential driving force Δμ at 303.15 K were 3.723 and 1656.453 J / mol, respectively;

[0099] (2) Substituting the supersaturation S into the following relationship, the three parameters a, b, and c are calculated to be 0.0463, 1.222, and 0.985 respectively.

[0100] (3) Substituting the parameters a, b, and c into equation (6), we have:

[0101]

[0102] The simultaneous equations (7) to (13) are used to solve the calcium ion concentration c1 at different crystallization times.

[0103] (4) Solve and experiment to obtain Ca at each time 2+ The concentrations are shown in Table 3:

[0104] time 0s 10s 30s 50s 80s 110s 150s 210s Calculated Value 46.40 34.92 29.19 27.95 27.03 26.46 25.95 25.42 Experimental value 46.40 33.67 31.63 30.10 29.34 28.06 26.79 26.02 time 5min 7min 9min 12min 15min 20min 30min 60min Calculated Value 24.89 24.41 24.05 23.67 23.41 23.05 22.59 21.89 Experimental value 25.51 24.59 24.29 23.47 22.70 22.45 21.94 22.19

[0105] The calculation results show that after 60 minutes, more than 50% of the Ca in the wastewater 2+was removed, approaching 93% of the thermodynamic limit of calcium sulfate crystallization in this water quality. Correlation between calculated value and experimental value (R 2 ) is 0.983.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater, characterized in that: The following steps are involved: Step 1: Obtain water quality indicators, and calculate the solution supersaturation S and initial chemical potential driving force Δμ0 through the water quality indicators; Step 2: Calculate the values ​​of parameters a, b, and c based on supersaturation; Step 3: According to the parameters a, b, c and the initial chemical potential driving force Δμ0, the calcium ion concentration values ​​at different crystallization times are calculated using the following formula: Where V represents the volume of the solution and c1 represents Ca 2+ concentration, T represents the thermodynamic temperature during crystallization, R represents the ideal gas constant, and Δμ represents the chemical potential driving force; Step 4: Based on the calculation results of step 3, determine the Ca content in the wastewater. 2+ The progress being removed.

2. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater according to claim 1, characterized in that: The supersaturation S value is between 1.2 and 8.

5.

3. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater according to claim 1, characterized in that: In step 2, the calculation formulas of parameters a, b, and c are: a=0.0021S 2 +0.00504S―0.00154; b=―0.17504S 2 +1.4570S―1.77625; c=0.02861S 2 +0.1046S+0.19947; Here, S represents the supersaturation of the solution.

4. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater according to claim 1, characterized in that: In step 1, the calculation formula of the solution supersaturation S is: Among them, IAP and K sp They represent the ion product and solubility product constants of calcium sulfate dihydrate in solution respectively.

5. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater according to claim 1, characterized in that: In step 1, the calculation formula of the initial chemical potential driving force Δμ0 is: in, and Respectively represent Ca 2+ and SO4 2- The ion activity in the bulk solution, and Respectively represent Ca 2+ and SO4 2- The activity of ions in a saturated solution.

6. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater according to claim 1, characterized in that: In the step 1, water quality indicators are obtained through testing.

7. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater according to claim 1, characterized in that: In step 1, the water quality indicators detected include: the ion product and solubility product constant of calcium sulfate dihydrate in the solution, Ca 2+ and SO4 2- The ion activity in the bulk solution, Ca 2+ and SO4 2- The activity of ions in a saturated solution.

8. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater according to claim 1, characterized in that: In step 3, the expression of the chemical potential driving force is: in, and Ca 2+ and SO4 2- The ionic activity coefficients of c1 and c2 represent the Ca 2+ and SO4 2- The concentration of and Respectively represent Ca 2+ and SO4 2- The activity of ions in a saturated solution.

9. A method for predicting the kinetics of calcium sulfate induced crystallization in wastewater according to claim 8, characterized in that: In step 3, Ca 2+ and SO4 2- The ion activity coefficient calculation formula is: Among them, z1 and z2 represent Ca 2+ and SO4 2- The ionic charge concentrations of α1 and β1 are Ca 2+ The first and second parameters, α2 and β2, are SO4 2- The first and second parameters of , A and B are the first and second coefficients respectively, and I is a constant related to the ion charge concentration in the solution, and its expression is: A=1.82×10 6 (εT) ―3 / 2 ; B=50.3(εT) ―1 / 2 ; ε is the dielectric constant of water, c i is the ion concentration in the solution, z i is the charge concentration of each ion in the solution.

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