CN102520043A - Method for accurately testing content of salt in seawater desalination liquid based on ion concentration and equipment special for method - Google Patents

Abstract

The invention relates to a method for accurately testing the content of salt in seawater desalination liquid based on ion concentration and equipment special for the method. By the method, an activity coefficient is corrected, measuring accuracy is improved, and the application range is expanded. Values of standard potential E<0> and slope S can be obtained through correction, a functional relation between the concentration of sodium ions in the seawater desalination liquid and the electromotive force of NaCl in the seawater desalination liquid is deduced according to a Nernst equation. During use, two indicating electrodes, namely a chloride ion selective electrode and a sodium ion glass electrode are used as a positive electrode and a negative electrode and are connected with an instrument to form a primary battery, the electromotive force of the seawater desalination liquid with unknown concentration is measured and substituted into the functional relation, and the display instrument can directly display the accurate concentration of the sodium ions in the seawater desalination liquid. The method is suitable for measuring low concentration in a narrow range, and is also suitable for accurately measuring the content of the salt in the seawater desalination liquid with high salt concentration, the accuracy of the method is higher than that of the conventional method, and a standard buffer solution is not required to be added in a linear range.

Description

A kind of method for accurate testing and specialized equipment thereof of the desalinization liquid salt content based on ion concentration

Technical field

The present invention relates to a kind of method for accurate testing and specialized equipment thereof of the desalinization liquid salt content based on ion concentration.

Technical background

Water resource is becoming a kind of scarce resource of preciousness, and water resources problems has been not only resource problem, more becomes the great strategic issue that is related to national economy, social sustainable development and long-term stability.Water has become another crisis after energy crisis of many countries.Under these circumstances, desalinization receives people's attention day by day.Desalinization promptly utilizes seawater desalination to produce fresh water, and as the increment technique of increasing income of water resource, desalinization has become the important channel that solves the water globe crisis of resource.Salinity how accurately to measure the seawater front and back is a desalting process important techniques link.The salinity of accurately measuring the seawater front and back can obtain through the situation of change of a certain ion such as Na ion concentration in the mensuration seawater, and the sodium ions content of so how accurately measuring in the seawater is the key of present technique.Ion-selective electrode is the activity of analytical solution intermediate ion or a kind of new analysis tool of concentration, is to develop one of analytical technology the most rapidly in the past few decades.At present measuring cell emf through ISE directly obtains the method for determinand content and mainly contains three kinds of direct comparison method, standard addition method and calibration curve methods.And use maximum at present is calibration curve method, is a kind of experience way but its shortcoming is it, does not consider the correction of activity coefficient, only is suitable for low concentration, concentration determination among a small circle.

To above situation, the present invention proposes the method for accurate testing and the specialized equipment thereof of former water of a kind of seawater based on ion concentration and desalination product (hereinafter to be referred as desalinization liquid) salinity.This method has been considered the correction of activity coefficient, has improved the precision and the scope of application measured, thereby can draw standard electrode potential E ⁰With the slope S value, calculate the activity coefficient of NaCl in the water by the Pitzer equation of simplifying (not considering interaction parameter), go out the functional relation between the electromotive force of NaCl in seawater desalination solution Na ion concentration and the desalinization liquid according to the Nernst equation inference thus.Therefore, in practical application,, just can directly draw Na ion concentration in the desalinization liquid by the electromotive force of NaCl in the desalinization liquid that records according to above-mentioned functional relation.This method not only is applicable to low concentration, concentration determination among a small circle, and is suitable for large-scale desalinization effect simultaneously and accurately measures, and degree of accuracy is higher, need not again in the range of linearity, need not to add standard buffer solution.Therefore, be the upgrade version of prior art.

Summary of the invention

The method for accurate testing and the specialized equipment thereof that the purpose of this invention is to provide a kind of desalinization liquid salt content based on ion concentration; It can the NaCl electromotive force directly draws the Na ion concentration in the seawater in the seawater through measuring, and confirms the salt content in the desalinization liquid with this.

For realizing above-mentioned target, technical scheme of the present invention is following:

A kind of method for accurate testing of the desalinization liquid salt content based on ion concentration, it is to be made up of measure portion-correction portion-hop-control section-five parts in display part, measuring principle such as Fig. 1, its step is following:

(1) in order to improve the stability of sodion glass electrode E2 and chloride ion-selective electrode E1, must carry out pre-service before the experiment, sodion glass electrode E2 is 10 in concentration ^-4Soaked 2 hours in the mol/LNaCl solution, chloride ion-selective electrode E1 is 10 in concentration ^-3Soaked 1 hour in the mol/LNaCl solution,

(2) select chloride ion-selective electrode E1 and two kinds of indicator electrodes of sodion glass electrode E2 to do both positive and negative polarity respectively; Connect and compose primary element with instrument I1 of the present invention (other parts except that measure portion, down together), temperature sensor T1 is connected with instrument I1 corresponding interface of the present invention; Be used to measure the temperature of liquid to be measured; Liquid to be measured is put into constant temperature water bath apparatus W1, be used to keep temperature be 25 ℃ constant

(3) standard solution of a series of different ionic strength (NaCl solution) is as correcting fluid; Put into constant temperature water bath apparatus; Obtain the relation of activity and electromotive force in a series of NaCl solution through measuring system, the correction of the activity coefficient that obtains through the Pitzer Equation for Calculating again draws the relation between concentration and the electromotive force by the Nernst equation; Proofread and correct through corrective system, draw standard electrode potential E ⁰With the value of slope S, the relative error of the theoretical slope in slope S and the Nernst equation can not surpass 1.5%, change otherwise carry out electrode,

(4) the standard electrode potential E that correction is obtained ⁰Be transferred to instrument I1 control section of the present invention with the value of slope S through hop; The combination of the correction of NaCl activity coefficient in the seawater that obtains with the Pitzer Equation for Calculating of simplifying; Draw in the desalinization liquid functional relation between the electromotive force of NaCl in the Na ion concentration and desalinization liquid theoretically by the Nernst equation

(5) in the practical application; Only need do both positive and negative polarity respectively with chloride ion-selective electrode and two kinds of indicator electrodes of sodion glass electrode; Connect the formation primary element, through the electromotive force of NaCl in the desalinization liquid of measure portion mensuration unknown concentration, the functional relation that substitution is above-mentioned; Directly show the Na ion concentration in the desalinization liquid in instrument I1 of the present invention display part, can directly obtain the Na ion concentration in the desalinization liquid.

The method for accurate testing of above-mentioned a kind of desalinization liquid salt content based on ion concentration, what described NaCl solution activity coefficient computing method were selected is single electrolyte solution average ion activity coefficient computing method-Pitzer equation.NaCl solution and Pitzer Equation for Calculating with known Na ion concentration c obtain activity coefficient at this moment, return the relation that obtains NaCl solution activity coefficient and concentration c and are:

lgγ _±NaCl＝-0.5108×c ^0.5/(1+1.350×c ^0.5)+0.0437×c-0.0094×c ^1.5(1)

The activity coefficient of NaCl solution in the time of can obtaining different Na ion concentration c according to formula (1).

In addition, described correction portion adopts 25 ℃ of NaCl solution as correcting fluid, and as both positive and negative polarity, battery is following with sodion glass electrode and chloride ion-selective electrode:

Na-ISE|NaCl，H ₂O|Cl-ISE

Corresponding electromotive force E can be expressed as E=E ⁰+ 2Slg (c γ _{± NaCl}), S is the slope of E～lgc, can return to draw.

When ISE is confirmed the electrolyte solution activity coefficient, must compare the theoretical slope of deriving in S and the Nernst equation, among this paper, E ⁰With S all be the parameter of regulating, use least square method and confirm that the minimum value of following formula confirms E ⁰Value with S.

$\mathrm{RSS}=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(E_{i,\exp }-E_{i,\mathrm{cal}})}^2$

In the formula, N representes the number of experimental point, E _{I, exp}Be experiment value, E _{I, cal}Be calculated value.

Moreover described Nernst equation is E=E for NaCl solution ⁰+ Slg (c (Na ⁺) c (Cl ^-) (γ _{± NaCl}) ²), and for the former water of seawater and the desalination product be E ^Sw=E ⁰+ Slg (c (Na ⁺) ^SwC (Cl ^-) ^Sw(γ ^Sw _{± NaCl}) ²).

The method for accurate testing of above-mentioned a kind of desalinization liquid salt content based on ion concentration, NaCl activity coefficient and Na ion concentration relation are lg γ in the desalinization liquid that the Pitzer equation that described utilization is simplified obtains ^Sw _{± NaCl}=-0.63173 * c ^0.5/ (1+1.872915 * c ^0.5)+0.011514 * c+0.023415 * c ^1.5, c representes Na ion concentration in the formula.

The method for accurate testing of above-mentioned a kind of desalinization liquid salt content based on ion concentration is describedly drawn theoretically in the desalinization liquid by the Nernst equation that the functional relation between the electromotive force of NaCl does in the Na ion concentration and desalinization liquid

$E^{\mathrm{sw}}=E^0+\mathrm{Slg}\left({\left({{\mathrm{\&gamma;}}^{\mathrm{sw}}}_{\&PlusMinus;\mathrm{NaCl}}\right)}^{2}c{\left({\mathrm{Na}}^{+}\right)}^{\mathrm{sw}}c{\left({\mathrm{Cl}}^{-}\right)}^{\mathrm{sw}}\right)$

$=E^0+S\&times;\left[\begin{array}{c}-1.26346\&times;c^{0.5}/(1+1.872915\&times;c^{0.5})+\\ 0.023028\&times;c+0.04683\&times;c^{1.5}+\lg \left(1.19816c^2\right)\end{array}\right]$

E in the following formula ⁰Obtain by the electrode correction with the value of S.Obtain in the desalinization liquid functional relation c=f (E between the electromotive force of NaCl in the Na ion concentration and seawater thus ^Sw).

The specialized equipment of the method for accurate testing of above-mentioned desalinization liquid salt content based on ion concentration; It is improved to ionometer (PXSJ-216; Shanghai Precision & Scientific Instrument Co., Ltd. Leici Instrument Factory); Increased correction portion, hop and control section, their circuit diagram is like dotted portion among Fig. 2, and dotted portion is the improved circuit diagram part to ionometer outward.The A part that wherein increases, it can realize amplifying circuit, amplifies (v to electric signal ₁～v ₂), voltage offset electric circuit (0～v ₁+ v ₂); The B that increases partly is the signal voltage modulate circuit, to satisfy the A/D voltage request; The C that increases partly is the Mega128 single-chip microcomputer, and wherein LCDLM12864 is a display; Keyboard is 4 * 4 series, comprises 0～9, radix point, carriage return and M ₁, M ₂Two functional blocks, the A/D module is digital-to-analog conversion, is converted into digital signal to electric analoging signal, program is in regression equation and the control program single-chip microcomputer EEprom storage unit to be arranged, and can store E ₀And S, during measuring, press M ₁Be the first step, at this moment K switch ₁And K ₃Link to each other with 2 positions with 1 respectively, this moment and original ionometer circuit form path, and electrode inserts as in 25 ℃ of NaCl solution of correcting fluid, calculates E by measuring-signal and SCM program ₀And S, output to the preservation of Mega128 single-chip microcomputer and show that on LCD LM12864 display its program is as shown in Figure 3, if greater than error range, change electrode and measure; If normal, got into for second step, press M ₂Be second step, K switch at this moment ₁And K ₂Link to each other with 2 positions with 1 respectively, electrode inserts in the seawater and measures, and calculates Na in the seawater by program after recording electromotive force ⁺Concentration c is also directly shown by LCD LM12864 display.Its program such as Fig. 3 and shown in Figure 4.

The method for accurate testing and the specialized equipment thereof of a kind of desalinization liquid salt content based on ion concentration of the present invention have following some superior part:

(1) this method is compared with ionometer, has increased correction portion, hop and software control part.Make it draw in the desalinization liquid functional relation c=f (E between the electromotive force of NaCl in the Na ion concentration and desalinization liquid theoretically ^Sw).Electromotive force E according to NaCl in the desalinization liquid that records ^Sw, directly show Na ion concentration c in the desalinization liquid by the display part.Compare with the direct demonstration reading of conventional ion densimeter, advantage has been to consider the correction of activity coefficient, and degree of accuracy improves greatly.This technology not only is applicable to low concentration, concentration determination among a small circle, and is suitable for the accurate mensuration of large-scale desalinization liquid salt content, need not again in the range of linearity, to need not to add standard buffer solution.

(2) this technology is compared with ion concentration, and the method for identifying chloride ion-selective electrode and sodion glass electrode quality is provided.This process is accomplished by corrective system, and judgment criterion is no more than 1.5% for proofreading and correct the slope S obtain and the relative error of the theoretical slope in the Nernst equation.

(3) this method uses chloride ion-selective electrode and two kinds of indicator electrodes of sodion glass electrode as both positive and negative polarity, rather than normally used indicator electrode and contrast electrode.Its advantage is to avoid that liquid connects the error effect that electromotive force causes in the contrast electrode.

Description of drawings

Fig. 1 is the principle schematic of the inventive method.

Fig. 2 is an electronic circuitry of the present invention.

Fig. 3 and Fig. 4 are related program among the present invention.

Fig. 5 is the synoptic diagram of the equipment therefor of this method, wherein: I1, instrument of the present invention (other parts except that measure portion); E1, chloride ion-selective electrode; E2, the sodion glass electrode; T1, thermopair; B1, beaker; W1, constant temperature water bath apparatus.

Embodiment

Through embodiment the present invention is specifically described below, but can not be interpreted as restriction scope of patent protection of the present invention.

Embodiment 1:

Prepare NaCl solution and the desalinization liquid of a series of ionic strengths between 0.0007～0.7mol/kg respectively; Wherein ionic strength is that the composition of the 0.7mol/kg desalinization liquid compound method that adopts the artificial seawater of Kester is [referring to Limnology & Oceanography; 1967; (12): 176-179], the desalinization liquid of other ionic strength adopts the method for dilution 0.7mol/kg desalinization liquid to obtain.Adopt the experimental provision like Fig. 5, wherein temperature is by constant temperature water bath apparatus W1 control, and I1 is an instrument of the present invention, and T1 is a thermopair, and E1 is a chloride ion-selective electrode, and E2 is the sodion glass electrode, and E1 and E2 and instrument I1 of the present invention connect and compose primary element.In order to improve the stability of sodion glass electrode E2 and chloride ion-selective electrode E1, must carry out pre-service before the experiment, sodion glass electrode E2 is 10 in concentration ^-4Soaked 2 hours in the mol/LNaCl solution, chloride ion-selective electrode E1 is 10 in concentration ^-3Soaked 1 hour in the mol/LNaCl solution.Sample is put into beaker B1, and temperature sensor T1 is used for monitor temperature, and its resolution is 0.1 ℃, makes temperature stabilization at 25 ℃.Carry out reading with display instrument I1 of the present invention, experimental data need be stablized in about about one minute, and deviation is no more than 0.5mV in half an hour, and the electromotive force value of writing down this moment is as experiment value.

As correcting fluid, the experimental data that draws is as shown in table 1 according to the NaCl solution between 0.0007～0.7mol/kg.

Different ionic strength NaCl-H during 25 ℃ in table 1 ₂Electromotive force value in the O binary system

Draw S=58.36 through correction portion, normal electrode E ⁰=143.76mV.Above-mentioned numerical value is transferred to control section through hop, in control section, can get according to the Nernst equation:

$E^{\mathrm{sw}}=E^0+\mathrm{Slg}\left({\left({{\mathrm{\&gamma;}}^{\mathrm{sw}}}_{\&PlusMinus;\mathrm{NaCl}}\right)}^{2}c{\left({\mathrm{Na}}^{+}\right)}^{\mathrm{sw}}c{\left({\mathrm{Cl}}^{-}\right)}^{\mathrm{sw}}\right)$

$=143.76+58.36\&times;\left[\begin{array}{c}-1.26346\&times;c^{0.5}/(1+1.872915\&times;c^{0.5})+\\ 0.023028\&times;c+0.04683\&times;c^{1.5}+\lg \left(1.19816c^2\right)\end{array}\right]$

NaCl electromotive force in the desalinization liquid that records by measure portion, and extrapolate Na ion concentration in the desalinization liquid, show directly that by Displaying Meter its value is the c (Na in the table 2 ⁺) cal.C (Na ⁺) exp for the preparation desalinization liquid in the sodion actual concentrations, the relative error between them is RE, the electromotive force of NaCl is E in the desalinization liquid ^Sw

The degree of accuracy of table 2 the present invention technology is identified

Can know that by relative error the degree of accuracy of the inventive method is very high, can accurately measure the salt content in the desalinization liquid.In the present embodiment, in order to narrate conveniently, thus write out detail calculation process, in the practical application, for same sodion glass electrode and chloride ion-selective electrode, slope S and standard electrode potential E ⁰Be constant, so this instrument directly shows the Na ion concentration in the desalinization liquid, detailed process need not manual calculation, only need directly carry out according to the program of finishing in the control section.

Claims (7)

1. method for accurate testing based on the desalinization liquid salt content of ion concentration, it is to be made up of measure portion-correction portion-hop-control section-five parts in display part, it is characterized in that it may further comprise the steps:

(1) in order to improve the stability of sodion glass electrode E2 and chloride ion-selective electrode E1, must carry out pre-service before the experiment, sodion glass electrode E2 is 10 in concentration ^-4Soaked 2 hours in the mol/LNaCl solution, chloride ion-selective electrode E1 is 10 in concentration ^-3Soaked 1 hour in the mol/LNaCl solution;

(2) select chloride ion-selective electrode E1 and two kinds of indicator electrodes of sodion glass electrode E2 to do both positive and negative polarity respectively, connect and compose primary element with instrument I1 of the present invention; Temperature sensor T1 is connected with instrument I1 corresponding interface of the present invention, is used to measure the temperature of liquid to be measured, and liquid to be measured is put into constant temperature water bath apparatus W1, be used to keep temperature be 25 ℃ constant;

(3) the NaCl standard solution of a series of different ionic strength is as correcting fluid; Put into constant temperature water bath apparatus; Obtain the relation of activity and electromotive force in a series of NaCl solution through measuring system, the correction of the activity coefficient that obtains through the Pitzer Equation for Calculating again draws the relation between concentration and the electromotive force by the Nernst equation; Proofread and correct through corrective system, draw standard electrode potential E ⁰With the value of slope S, the relative error of the theoretical slope in slope S and the Nernst equation can not surpass 1.5%, changes otherwise carry out electrode;

(4) the standard electrode potential E that correction is obtained ⁰Be transferred to instrument I1 control section of the present invention with the value of slope S through hop; The combination of the correction of NaCl activity coefficient in the seawater that obtains with the Pitzer Equation for Calculating of simplifying draws in the desalinization liquid functional relation between the electromotive force of NaCl in the Na ion concentration and desalinization liquid theoretically by the Nernst equation;

(5) in the practical application; Only need do both positive and negative polarity respectively with chloride ion-selective electrode and two kinds of indicator electrodes of sodion glass electrode; Connect the formation primary element, through the electromotive force of NaCl in the desalinization liquid of measure portion mensuration unknown concentration, the functional relation that substitution is above-mentioned; Display part at instrument I1 of the present invention directly shows the Na ion concentration in the desalinization liquid, can directly obtain the Na ion concentration in the desalinization liquid.

2. the method for accurate testing of desalinization liquid salt content according to claim 1; It is characterized in that: what NaCl solution activity coefficient computing method were selected is single electrolyte solution average ion activity coefficient computing method-Pitzer equation; NaCl solution and Pitzer Equation for Calculating with known Na ion concentration c obtain activity coefficient at this moment, return the relation that obtains NaCl solution activity coefficient and concentration c and are:

lgγ _±NaCl＝-0.5108×c ^0.5/(1+1.350×c ^0.5)+0.0437×c-0.0094×c ^1.5(1)

The activity coefficient of NaCl solution in the time of can obtaining different Na ion concentration c according to formula (1).

3. the method for accurate testing of desalinization liquid salt content according to claim 1 is characterized in that: described corrective system adopts 25 ℃ of NaCl solution as correcting fluid, and as both positive and negative polarity, battery is following with sodion glass electrode and chloride ion-selective electrode:

Na-ISE|NaCl，H ₂O|Cl-ISE

Corresponding electromotive force E can be expressed as E=E ⁰+ 2Slg (c γ _{± NaCl}), S is the slope of E～lgc, can return to draw;

When ISE is confirmed the electrolyte solution activity coefficient, must compare the theoretical slope of deriving in S and the Nernst equation, E ⁰With S all be the parameter of regulating, use least square method and confirm that the minimum value of following formula confirms E ⁰Value with S:

$\mathrm{RSS}=\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{(E_{i,\exp }-E_{i,\mathrm{cal}})}^2$

In the formula, N representes the number of experimental point, E _{I, exp}Be experiment value, E _{I, cal}Be calculated value.

4. the method for accurate testing of desalinization liquid salt content according to claim 1 is characterized in that: described Nernst equation is E=E for NaCl solution ⁰+ Slg (c (Na ⁺) c (Cl ^-) (γ _{± NaCl}) ²), and for seawater and the desalination product be E ^Sw=E ⁰+ Slg (c (Na ⁺) ^SwC (Cl ^-) ^Sw(γ ^Sw _{± NaCl}) ²).

5. the method for accurate testing of desalinization liquid salt content according to claim 1 is characterized in that: NaCl activity coefficient and Na ion concentration relation are lg γ in the desalinization liquid that the Pitzer equation that described utilization is simplified obtains ^Sw _{± NaCl}=-0.63173 * c ^0.5/ (1+1.872915 * c ^0.5)+0.011514 * c+0.023415 * c ^1.5, c representes Na ion concentration in the formula.

6. the method for accurate testing of desalinization liquid salt content according to claim 1 is characterized in that: describedly drawn theoretically in the desalinization liquid by the Nernst equation that the functional relation between the electromotive force of NaCl does in the Na ion concentration and desalinization liquid

$E^{\mathrm{sw}}=E^0+\mathrm{Slg}\left({\left({{\mathrm{\&gamma;}}^{\mathrm{sw}}}_{\&PlusMinus;\mathrm{NaCl}}\right)}^{2}c{\left({\mathrm{Na}}^{+}\right)}^{\mathrm{sw}}c{\left({\mathrm{Cl}}^{-}\right)}^{\mathrm{sw}}\right)$

$=E^0+S\&times;\left[\begin{array}{c}-1.26346\&times;c^{0.5}/(1+1.872915\&times;c^{0.5})+\\ 0.023028\&times;c+0.04683\&times;c^{1.5}+\lg \left(1.19816c^2\right)\end{array}\right]$

E in the following formula ⁰Proofread and correct by electrode with the value of S and to obtain, obtain in the desalinization liquid functional relation c=f (E between the electromotive force of NaCl in the Na ion concentration and desalinization liquid thus ^Sw).

7. the specialized equipment of the method for accurate testing of the described desalinization liquid of claim 1 salt content; Characteristic is: it is improved to ionometer, has increased correction portion, hop and control section, the A part that wherein increases; It realizes amplifying circuit, amplifies (v to electric signal ₁～v ₂), voltage offset electric circuit (0～v ₁+ v ₂); The B that increases partly is the signal voltage modulate circuit, to satisfy the A/D voltage request; The C that increases partly is the Mega128 single-chip microcomputer, and wherein LCD LM12864 is a display; Keyboard is 4 * 4 series, comprises 0～9, radix point, carriage return and M ₁, M ₂Two functional blocks; The A/D module is digital-to-analog conversion, is converted into digital signal to electric analoging signal, and program is in regression equation and the control program single-chip microcomputer EEprom storage unit to be arranged, and can store E ₀And S, during measuring, press M ₁Be the first step, at this moment K switch ₁And K ₃Link to each other with 2 positions with 1 respectively, this moment and original ionometer circuit form path, and electrode inserts as in 25 ℃ of NaCl solution of correcting fluid, calculates E by measuring-signal and SCM program ₀And S, output to the preservation of Mega128 single-chip microcomputer and show that on the LCDLM12864 display its program is following:

If the result greater than error range, changes electrode and measures; If normal, got into for second step, press M ₂Be second step, K switch at this moment ₁And K ₂Link to each other with 2 positions with 1 respectively, electrode inserts in the seawater and measures, and calculates Na in the seawater by program after recording electromotive force ⁺Concentration c also directly shows that by LCD LM12864 display its program is following:

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