CN102590470B - Method for determining dissolving state and adsorption state of Pb (II) in mineral soil - Google Patents

Abstract

The invention provides a method for determining dissolving state and adsorption state of Pb (II) in mineral soil, and belongs to the field of soil analysis. The method comprises the steps: separating clay minerals from the soil, testing the CEC (cation exchange capacity) value and the specific surface area Ss of the minerals, testing acid-base constants (namely logK(+), logK(-) and logK(Na, H)) of the surface of the clay minerals, testing metal complexion constants (namely logK(AlOPb) and logK(X2Pb)) of the surface of the clay minerals, testing weight percentages of organic matters, iron oxide and clay granules in the soil, and constructing a full-soil model. According to the method for determining dissolving state and adsorption state of Pb (II) in the mineral soil, the problem that the states of Pb in the soil cannot be predicated is solved, the determination method for the state and the concentration of Pb in a soil system is created, and the method can be used for predicating the effective concentration of Pb in the mineral soil.

Description

A kind of definite method of Pb (II) solubilised state and ADSORPTION STATE in mineral soil

Technical field

The present invention relates to a kind of definite method of calculating heavy metal Pb (II) occurrence patterns in mineral soil, specifically, refer to a kind of based on chemical substance homeostasis model and the chemical equilibrium at solid phase of soil Surface Complexation Model in aqueous solution determine method.

Background technology

In soil, " form " of metal (speciation) refers to the various occurrence types of heavy metal in soil.The influence degree of migration, conversion and the murder by poisoning to plant and the environment of heavy metals in soil, outside the Pass having with the total content of heavy metal in soil, also the form that exists in soil has much relations with metallic element.

Metal exists with variform in soil.Some form is Yi Rong, and some form is inertia, as is combined in the part in mineral lattice.Inertia form affects its biology hardly to property or eco-toxicity, and with the soil of eco-toxicity significant correlation in the main form that exists of metal comprise: 1) be present in the soil liquid with solubilised state, although it is very little that the metal of this form accounts in soil the share of total metal content, but movability and biological effectiveness are the highest, it is the Main Morphology of bio-absorbable metal; 2) be adsorbed on solid phase of soil surface, in soil, have multiple solid phase, all exist in a large number can adsorbing metal ions active site position, some ADSORPTION STATE metals are when condition is applicable easily again under desorb, enter in the soil liquid, therefore this form is usually served as the role of " bank ".

The method of research species of heavy metals in soil mainly contains traditional continuous extraction, single or fractional extraction method, isotopic dilution exchange process, original position passive sampling method etc.But because mostly these methods are to adopt certain chemical extraction agent, also have the problem such as the reallocation of absorption again of trace-metal in leaching process, making defining of its form is a kind of Operation Definition, cannot reflect soil in the true form of metal.

In recent years the chemical form of metal stable state in aqueous solution is determined to method has had large development, as the MINTEQ program of U.S. EPA exploitation can be used for the concentration of each material under calculated equilibrium condition.The absorption-desorption process of simulation metallic ion at solid phase of soil colloid surface and calculate the pollutant key that form distributes in soil, comprising the absorption on SOIL CLAY MINERALS, iron and manganese oxides and agron surface, and for mineral soil, at the main process that is adsorbed as on the above two surfaces.

In the past few decades, the people such as Stern and Stumm have been developed Surface Complexation Model (SurfaceComplexation Model, SCM) and have been described the absorption behavior of ion at mineral surface.SCM model is described as one or more surface complex reactions by ion at the absorption behavior of mineral surface.The model of common description mineral surface electrostatic attraction comprises diffusion layer model (DLM), electrostatic double layer model (BSM), three electric layer models (TLM) and permanent capacitor model (CCM).Up to the present, the Adsorption Model research on soil oxide mineral is more ripe, and aluminum silicate clay mineral is also had carried out some research, and found that SCM can better describe the absorption behavior of ion at mineral surface.

More than research is all taking certain one-component in soil as research object, still rare for the comprehensive morphological model investigation of soil system.

Summary of the invention

1. the technical matters that invention will solve

In mineral soil, the biologically effective form of Pb in soil is mainly soluble state and ADSORPTION STATE, and wherein the existing geochemical balance model of soluble state Pb can carry out the calculating of corresponding form; And simulation ADSORPTION STATE Pb is the key of setting up P in soil b and determine method, the invention provides definite method of (II) solubilised state of Pb in a kind of mineral soil and ADSORPTION STATE, ADSORPTION STATE Pb is divided into the absorption on layered silicate clay mineral (hereinafter to be referred as clay mineral), ferriferous oxide, the soil organism, adopt respectively SCM to simulate its adsorption reaction, measure adsorption reaction constant and correlation parameter, three kinds of adsorbing medium points position is defined, built the geochemical balance model of solubilised state and ADSORPTION STATE Pb in complete mineral soil and determine method.

2. technical scheme

The absorption of inventive principle: Pb in mineral soil is mainly put position for layered silicate clay mineral and ferriferous oxide colloid.The former is because soil parent material is different different with rate of decay, and composition and character are also different, and with surface charge of different nature.The generation more complicated of clay mineral surface charge, not only comprises the variable charge that mineral edge is produced by hydroxyl proton or deprotonation, and the permanent negative charge that also has isomorphous substitution to form.Universal model is difficult to simulation, and the present invention adopts two point position method to set up Pb at the SCM Adsorption Model on soil clay mineral surface and the assay method of absorption constant.And Iron in Soil oxide colloid is because structure is more single, more abundant to the research of its adsorption character, can, by searching document, obtain corresponding constant.Various equilibrium constant values and absorption constant on the soil organism the also existing bibliographical information of Pb in aqueous solution, can directly use in addition.

Geochemical balance modular concept is as follows:

Geochemical balance model is the theory based on chemical reaction and chemical thermodynamics growing up in generation nineteen sixty, application of mathematical method, and computer technology is carried out model solution, draws the method that has form and concentration of chemical composition in research system.

For a water solubilised state Chemical Equilibria Systems, there is a mass action equation corresponding to each complex ion:

${\mathrm{lga}}_i-\underset{j=1}{\overset{J}{\mathrm{\Σ}}}{c}_{i,j}\·{\mathrm{lga}}_j={\mathrm{lgK}}_i$

Each element is to there being a quality to keep weighing apparatus equation:

$\underset{i=1}{\overset{I}{\mathrm{\Σ}}}{c}_{i,j}\·m_i={\mathrm{TOT}}_j$

Wherein: a _ithe concentration of-i kind complex compound;

A _jthe concentration of-j kind component ion;

C _{i, j}-the stoichiometric number of j kind component ion in the water-soluble species of i kind;

K _ithe equilibrium constant an of-i complex reaction;

M _ithe concentration of-i kind the hydrotrope;

TOT _jthe total concentration of-corresponding j component ion.

Keep the combination of weighing apparatus equation based on above mass action equation and quality, can obtain one group of nonlinear equation, if the equilibrium constant K of known each complex reaction _i, and the total concentration TOT of every kind of component ion _j, use conventional Linear Algebraic Method to solve, obtain the concentration value a of every kind of complex compound _i.

SCM modular concept is as follows:

The free energy of surface engagement reaction can be divided into chemical energy and electrostatic energy.For example proton can be described below at combination and the separating reaction of oxide surface:

The equilibrium constant of reaction can be expressed as follows:

$K_{(+)}^{\mathrm{inc}}_c=\frac{[\≡{\mathrm{SOH}}_2^{+}]}{[\≡{\mathrm{SOH}}^D]\left[H^{+}\right]{\mathrm{\γ}}_{H^{+}}}\exp ({\mathrm{\ψ}}_{s}F/\mathrm{RT})---\left(3\right)$

$K_{(-)}^{\mathrm{inc}}_c=\frac{[\≡{\mathrm{SO}}^{-}]\left[H^{+}\right]{\mathrm{\γ}}_{H^{+}}}{[\≡{\mathrm{SOH}}^D]}\exp (-{\mathrm{\ψ}}_{s}F/\mathrm{RT})---\left(4\right)$

Wherein " ≡ " presentation surface point position, square bracket represent the concentration (mol/L) of each material, γ is activity coefficient, can be obtained by Davies Solving Equations exp (ψ _sf/RT) come from Boltzmann equation, for adjusting the electrostatic attraction of powered surfaces.ψ _sbe surface charge (V), F is faraday constant 96487C mol ^-1, R is calibrating gas constant 8.314J mol ^-1k ^-1, T is absolute temperature (K).If adsorption site figure place Ns (mol/L) can measure, the mass balance equation of a description list millet cake position is as follows:

$N_S=[\≡{\mathrm{SOH}}_2^{+}]+[\≡{\mathrm{SOH}}^0]+[\≡{\mathrm{SO}}^{-}]---\left(5\right)$

Surface charge density σ (C m ^-2) can be described as:

$G=\frac{\left(\right[\≡{\mathrm{SOH}}_2^{+}]-[\≡{\mathrm{SO}}^{-}\left]\right)F}{S_s{S}_d}---\left(6\right)$

Wherein: Ss is specific surface area (m ²g ^-1), it can pass through N ₂/ BET specific surface method is measured, S _dthe suspension concentration (gL of solid ^-1).

According to permanent electric capacity (CCM) model, σ and ψ have following relation:

σ _o＝κψ _s (7)

Wherein κ is a constant, presentation surface electric capacity (Farad m ^-2)

Have 5 unknown numbers: [≡ SOH ⁰], [≡ SOH ₂ ⁺], [≡ SO ^-], σ and ψ _s, also there are 5 equation: 3-7, therefore can obtain this 5 unknown numbers, comprise the concentration value of 3 configurations of surface.

Therefore, SCM model also can be regarded the special geochemical balance model of a class as, keeps weighing apparatus equation, the equilibrium constant K of known response based on mass action equation and quality _itotal concentration TOT with each component _j, can use conventional Linear Algebraic Method to solve the concentration value a of every kind of complex compound _i.

According to the source difference of soil clay mineral surface charge, adopt two point position method, clay mineral is divided into two some positions to the absorption of Pb: the permanent negative charge ≡ X of the variable charge ≡ AlOH at mineral edge and interlayer ^-.Mineral surface reaction comprises following 5 reactions (table 1).

Table 1.Pb is in the reaction on soil clay mineral surface

The crucial constant that clay total surface adsorption site figure place Ns (mol/L) needs for model, the cation exchange capacity (CEC) (CEC) when the present invention adopts pH=8, permanent negative charge ≡ X ^-the CEC value of some figure place while being pH=4, the some figure place of variable charge ≡ AlOH is CEC value poor of pH=8 and pH=4.

Similarly, if know that the Pb of above-mentioned equation is in the reaction constant value on soil clay mineral surface, the corresponding concentration value of each configuration of surface can calculate balance time.

The thinking of measuring clay mineral surface reaction constant value is as follows, first isolates soil clay mineral, adopts the soda acid constant value logK on potentiometric determination clay mineral surface _(+),, logK _(-),and logK _{(Na, H)}, then adopt batch adsorption experiment to measure Pb adsorbance under different pH condition on clay mineral, simulate the absorption constant value logK of Pb on clay mineral surface _(AlOPband logK _(X2Pb), by searching document, obtain various equilibrium constant values and the absorption constant ferriferous oxide and the soil organism on of Pb in aqueous solution, finally set up Pb form in complete soil and determine method.

1. a definite method for Pb (II) solubilised state and ADSORPTION STATE in mineral soil, comprises the following steps:

The first step: separate soil clay mineral, measure CEC value and the specific surface area S of mineral _s:

1) acetic acid/sodium acetate buffer solution removal carbonate;

2) sodium hydrosulfite is removed ferriferous oxide;

3) hydrogen peroxide is removed organic;

4) sedimentation is collected the soil clay mineral of < 2 μ m;

5) adopt dialysis pickling, Na ion saturated mineral surface;

6) measure the cation exchange capacity (CEC) CEC value under pH=4 and pH=8 condition, N ₂-BET method is measured mineral specific surface area S _s.

Second step: the soda acid constant value logK on potentiometric determination clay mineral surface ₍₊₎, logK _(-)and logK _{(Na, H)}: adopt two point position method, clay mineral is divided into two some positions to the absorption of Pb: the permanent negative charge ≡ X of the variable charge ≡ AlOH at mineral edge and interlayer ^-, adopt the electrostatic attraction on permanent capacitor C CM models fitting surface, adopt automatical potentiometric titrimeter and back titration method to obtain the titration curve of clay mineral, substitution nonlinear optimization program FITEQL ver3.1 carries out matching and measures the soda acid constant value logK on clay mineral surface ₍₊₎, logK _(-)and logK _{(Na, H)}, reactional equation is as follows:

logK ₍₊₎

logK _(-)

logK _(Na，H)

The 3rd step: batch adsorption experiment method is measured the metal complex constant logK on clay mineral surface _(AlOPb)and logK _(X2Pb): adopt batch adsorption experiment method to measure the adsorption curve under different pH values or ionic strength conditions, substitution FITEQLver3.1 simulates the metal surface complex reaction constant value logK of Pb on soil clay mineral surface _(AlOPb)and logK _(X2Pb), surface reaction equation is as follows:

logK _(AlOPb)

logK _(X2Pb)

The 4th step: measure the weight percent content of organic matter, ferriferous oxide and the clay mineral of soil, build full soil model

For research soil, measure soil parameters, comprising: soil pH value, soil organic matter content OM%, the soil texture, soil clay mineral content clay%, soil ferriferous oxide content F e ₂o ₃hNO when % and pH=2 ₃extract Pb concentration in soil, and the CEC value of the mineral of measuring in above-mentioned steps and specific surface area S _sthe metal surface complex reaction constant on the soda acid constant value on clay mineral surface and clay mineral surface, according to Pb at the adsorption reaction on ferriferous oxide surface and Pb the adsorption reaction relation on organic surface, from document, Pb (II) adopts permanent capacitor C CM model on soil ferriferous oxide goethite surface, and at the organic surperficial electrostatic double layer BSM model that adopts two point position, corresponding reaction constant and model parameter are in table 5

Pb in the adsorption reaction on ferriferous oxide surface is:

logK _int＝7.47

logK _int＝-9.51

logK _int＝-0.17

logK _int＝-8.85

Pb in the adsorption reaction on organic surface is:

logK _int＝-2.75

logK _int＝-7.5

logK _int＝1.8

logK _int＝0.65

logK _int＝-6.23

logK _int＝1.25

logK _int＝-5.68

Search the equilibrium constant value of Pb in solution in document, SCM model in conjunction with Pb on the each solid phase components of soil, create the stoichiometry matrix table (table 6) that in soil, Pb form is calculated and build full soil model, this matrix is laterally the mass action system of equations that geochemical balance model needs, and keeps weighing apparatus system of equations and be longitudinally quality.

The complete native appearance model chemistry stoichiometric matrix table of table 6.Pb

Form	AlOH	exp(l)	FeOH	exp(2)	X.Na	Pb	S 1H	S 2H	exp(0)	exp(d)	H 2L	Cl	SO 4	CO 2	Na	H	logK
																		Pb 2+	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	0	0
PbOH +	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	-1	-7.68
																		Pb(OH) 2	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	-2	-17.17
PbHCO 3 +	0	0	0	0	0	1	0	0	0	0	0	0	0	1	0	-1	-4.648
																		PbCO 3	0	0	0	0	0	1	0	0	0	0	0	0	0	1	0	-2	-11.348
PbCl +	0	0	0	0	0	1	0	0	0	0	0	1	0	0	0	0	1.56
																		PbSO 4	0	0	0	0	0	1	0	0	0	0	0	0	1	0	0	0	2.69
PbL	0	0	0	0	0	1	0	0	0	0	1	0	0	0	0	-2	-5.16
																		≡FeOPb	0	0	1	1	0	1	0	0	0	0	0	0	0	0	0	-1	-0.17
≡FeOPbOH	0	0	1	0	0	1	0	0	0	0	0	0	0	0	0	-2	-8.85

≡AlOPb	1	1	0	0	0	1	0	0	0	0	0	0	0	0	0	-1	logK (AlOPb)
																		≡X 2.Pb	0	0	0	0	2	1	0	0	0	0	0	0	0	0	-2	0	logK (X2Pb)
≡S 1Pb	0	0	0	0	0	1	1	0	1	0	0	0	0	0	0	-1	0.65
																		≡S 1PbOH	0	0	0	0	0	1	1	0	0	0	0	0	0	0	0	-2	-6.23
≡S 2Pb	0	0	0	0	0	1	0	1	1	0	0	0	0	0	0	-1	1.25
																		≡S 2PbOH	0	0	0	0	0	1	0	1	0	0	0	0	0	0	0	-2	-5.68
H 2CO 3	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	-1.47
																		HCO 3 -	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	-1	-7.83
CO 3 2-	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	-2	-18.16
																		Cl -	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0
SO 4 2-	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0
																		H 2L	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0
HL -	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	-1	-3.65
																		L 2-	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0	-2	-8.81
Na +	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0
																		≡FeOH 2	0	0	1	1	0	0	0	0	0	0	0	0	0	0	0	1	7.47
≡FeOH	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
																		≡FeO -	0	0	1	-1	0	0	0	0	0	0	0	0	0	0	0	-1	-9.51
≡AlOH 2 +	1	1	0	0	0	0	0	0	0	0	0	0	0	0	0	1	logK (+)
																		≡AlOH	1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
≡AlO -	1	-1	0	0	0	0	0	0	0	0	0	0	0	0	0	-1	logK (-)
																		≡X -.Na +	0	0	0	0	1	0	0	0	0	0	0	0	0	0	0	0	0
≡X -.H +	0	0	0	0	1	0	0	0	0	0	0	0	0	0	-1	1	logK (Na，H)
																		≡S 1H	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	0
≡S 1 -	0	0	0	0	0	0	1	0	-1	0	0	0	0	0	0	-1	-2.75
																		≡S 2H	0	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0
≡S 2 -	0	0	0	0	0	0	0	1	-1	0	0	0	0	0	0	-1	-7.5
																		≡S 2H 2 +	0	0	0	0	0	0	0	1	1	0	0	0	0	0	0	1	1.8
OH -	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	-1	-14
																		H +	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0

Quality is kept the total concentration value that weighing apparatus system of equations needs each component.Wherein the total concentration of Pb is learnt by mensuration; Dissolved Organic Matter H ₂l, SO ₄ ^2-, Cl ^-little on result of calculation impact, be respectively 1*10 ^-5m, 1*10 ^-5m, 6*10 ^-5m; Na ⁺concentration is determined by background dielectric value solution concentration.And clay mineral in soil, ferriferous oxide, organic absorption always to put figure place be to calculate required important parameter.According to document and experimental result, each solid phase adsorption point site concentration Ns (mol/L) is respectively:

Clay mineral:

Ns _(≡AlOH)＝M％S _d*(CEC ₈-CEC ₄)*10 ^-5

Ns _(≡X-.H+)＝M％S _d*CEC ₄*10 ^-5

Ferriferous oxide:

Ns _(≡FeOH)＝M％S _d*13.56*10 ^-5

The soil organism:

Ns _(≡S1)＝M％S _d*255*10 ^-5

Ns _(≡S2)＝M％S _d*63*10 ^-5

Wherein M% is the mass percent of each solid phase components in soil, S _dfor suspension concentration (g/L), CEC ₈and CEC ₄cEC value (the cmol kg of the soil clay mineral while being respectively pH=8 and pH=4 ^-1).

According to the stoichiometry matrix table of table 6, the concentration of each form when help that can computer calculates balance, thus obtain the ADSORPTION STATE concentration of Pb at the soil liquid and each solid phase surface.

3. beneficial effect

The invention solves the unpredictable problem of form of heavy metal in soil Pb, on geochemical balance model basis in solution, add the surface complexation SCM model on solid phase of soil surface, the different solid phase surface point bit classes of soil, concentration, surface reaction, surface electrostatic gravitation are defined, create definite method of Pb form concentration in soil system, obtain effect and can be used for the prediction of available state Pb concentration in mineral soil, administer reference is provided for heavy metal-polluted soil ecological risk assessment and soil pollution.

Brief description of the drawings

Fig. 1 is for making titration system structural texture schematic diagram by oneself: in figure, mark 1-constant water bath box (temperature is controlled at 25+0.5 DEG C), 2-current potential stirrer, 3-water inlet, 4-nylon ring, 5-N ₂air intake opening, 6-pH electrode, the double-deck a set of cups of 7-stainless steel, 8-water delivering orifice, 9-the first buret, 10-the second buret, 11-computing machine, the wherein double-deck a set of cups 7 of 100ml tygon beaker outer casing stainless steel, tygon beaker is connected with constant water bath box 1 with water delivering orifice 8 by water inlet 3, the rim of a cup of tygon beaker is provided with nylon ring 4, N ₂air intake opening 5, current potential stirrer 2, pH electrode, the first buret 9, the second buret 10 are connected with beaker by nylon ring 4, automatical potentiometric titrimeter control the first buret 9, the second buret 10, the first burets 9, the second buret 10 add respectively 0.1000M HNO ₃with 0.0200M NaOH solution, the controllable minimum liquid volume added of instrument is 0.2 μ l, titrator is controlled a current potential stirrer 2 with maintenance system homogeneity simultaneously, the pH electrode 6 that titration is used is the Ag/AgCl combination electrode of plum Teller-Tuo benefit, electrode precision is 0.001pH unit, constantly passes through N in titration process in suspending liquid ₂air intake opening is filled with high pure nitrogen and drives CO ₂, current potential stirrer 2, pH electrode 6, the first buret 9, the second buret 10 are connected with computing machine 11;

Fig. 2 black earth clay mineral potentiometric titration curve figure;

Fig. 3 red soil clay mineral potentiometric titration curve figure;

Fig. 4 yellowish soil clay mineral potentiometric titration curve figure;

At the absorption behavior on red soil clay mineral surface and models fitting result figure, (ordinate is Pb absorption number percent to Fig. 5 Pb, wherein solid line, dotted line, dotted line represents respectively I=0.001M, 0.01M, fitting result under 0.1M, square, circle, triangle represents I=0.001M, 0.01M, the experimental data under 0.1M, back-ground electolyte is NaNO ₃, Sd=4g/l);

At the absorption behavior on yellowish soil clay mineral surface and models fitting result figure, (ordinate is Pb absorption number percent to Fig. 6 Pb, wherein solid line, dotted line, dotted line represents respectively I=0.001M, 0.01M, fitting result under 0.1M, square, circle, triangle represents I=0.001M, 0.01M, the experimental data under 0.1M, back-ground electolyte is NaNO ₃, Sd=4g/l);

At the absorption behavior on black earth clay mineral surface and models fitting result figure, (ordinate is Pb absorption number percent to Fig. 7 Pb, wherein solid line, dotted line, dotted line represents respectively I=0.001M, 0.01M, fitting result under 0.1M, square, circle, triangle represents I=0.001M, 0.01M, the experimental data under 0.1M, back-ground electolyte is NaNO ₃, Sd=4g/l);

(ordinate is Pb absorption number percent, and round dot is experimental data, and solid line is result of calculation, I=0.01MNaNO for the adsorption experiment of Pb on red soil clay mineral and comparison of computational results figure under Fig. 8 different pH condition ₃);

(ordinate is Pb absorption number percent, and round dot is experimental data, and solid line is result of calculation, I=0.01MNaNO for the adsorption experiment of Pb on yellowish soil clay mineral and comparison of computational results figure under Fig. 9 different pH condition ₃);

(ordinate is Pb absorption number percent, and round dot is experimental data, and solid line is result of calculation, I=0.01MNaNO for the adsorption experiment of Pb on black earth clay mineral and comparison of computational results figure under Figure 10 different pH condition ₃).

Embodiment

Embodiment 1: the invention will be further described by the following examples:

Adopt above method, select three kinds of representative soil of China: Red Soil, Nanjing yellowish soil, Heilungkiang black earth are research object.First taking Red Soil as example:

The first step: separate soil clay mineral, measure CEC value and the specific surface area S of mineral _s.

Soil clay extracts according to the following steps:

1) remove carbonate

Method: take air-dry soil that 20g crosses 2mm sieve in the centrifuge tube of 250ml, add 120ml1M acetate/acetic (pH value is 5) buffer solution, shake and spend the night on shaking table, then centrifugal 20 minutes of 7500rpm, outwells supernatant.

2) remove ferriferous oxide

Method: give in above-mentioned sample after centrifugal and add 50ml0.28M sodium citrate, 0.1M sodium bicarbonate buffer solution, in water-bath, 70 DEG C of water-baths 2 hours, then add 1g sodium hydrosulfite, after swaying 1 minute, leave standstill half an hour.Centrifugal 10 minutes of last 7500rpm, outwells supernatant.

3) remove organic matter

Method: will put in the beaker in tall form of 800ml through the sample of step process above, the hydrogen peroxide that the percent by volume that adds 50ml is 12% spends the night (once there be foam overflow, just adding several sec-n-octyl alcohols).Careful heats on electric hot plate, until a large amount of lather collapses will stir in the process of heating always, prevents violent bubbling.If organism is not also removed totally, after carry sample is cooling, continue to add 10ml hydrogen peroxide, until all organic substances are all removed.

4) collect soil clay

Clay sample is disperseed with deionized water, then the suspension disperseing is filtered by the sieve of 53 μ m (270 order).Clay part (the natural subsidence that < 2 μ particle m) is undertaken by Stokes' law.In general, the particle of > 2 μ m can sedimentation 30cm in 24 hours, and suspending liquid is above exactly the clay part that will collect, extracts suspension out by siphon, finally adds enough 0.5M Mg (NO ₃) ₂solution is by clay flocculating setting.

5) purifying

Disturb and remove easy molten part in order to reduce impurity, adopt pickling clay and Na ⁺ion saturated clay surface.Concrete steps are as follows: clay suspension is put into bag filter, be immersed in pH and be 3 (with HNO ₃regulate) 0.5MNaNO ₃in solution 2 hours, afterwards Acidwash solution is outwelled, continue to add 0.5M NaNO ₃solution, and regulate pH to the natural pH. of clay with NaOH, this sodium nitrate solution need to change three times, at every turn balance two hours at least.Last unnecessary salt is washed 10 times with deionized water, then by after the freeze drying of clay sample with for subsequent use.CEC while measuring pH=4 and pH=8, adopts N ₂-BET method measurement the specific area.Nanjing yellowish soil, the same Red Soil of Heilungkiang black earth implementation step

Isolate three kinds of clay mineral components in soil, and the physicochemical property of soil and clay mineral is measured, the results are summarized in table 2.

The basic physical and chemical summary sheet of three kinds of soil of table 2 and clay composition thereof

The soda acid constant value on second step potentiometric determination clay mineral surface is taking Red Soil as example, Nanjing yellowish soil, the same Red Soil of Heilungkiang black earth implementation step):

Adopt intelligent potentiometric titrimeter to be: plum Teller-Tuo benefit automatical potentiometric titrimeter T70.

Make by oneself shown in titration system structure in conjunction with Fig. 1, experiment suspending liquid is placed in to 100ml tygon beaker, the double-deck a set of cups of beaker outer casing stainless steel, is connected with constant water bath box.By 2 burets of automatical potentiometric titrimeter control, add respectively 0.1000M HNO ₃with 0.0200M NaOH solution, the controllable minimum liquid volume added of instrument is 0.2 μ l, and titrator is controlled a current potential stirrer with maintenance system homogeneity simultaneously.The Ag/AgCl combination electrode that the pH electrode that titration is used is plum Teller-Tuo benefit, electrode precision is 0.001pH unit.In titration process, in suspending liquid, be constantly filled with high pure nitrogen and drive CO ₂.

The alkali that titration is used adopts Potassium Hydrogen Phthalate to demarcate, and acid is demarcated with the alkali of demarcating.PH electrode adopts pH buffer solution (4.01,7.00,10.01) to proofread and correct.

Accurately take 0.16g sample and add in titration cup, add 40ml 0.01M NaNO ₃back-ground electolyte, passes into nitrogen two hours to drive CO ₂.First carry out titration with the nitric acid of 0.1M, the rate of change of setting pH is balance while within every 5 seconds, being less than 0.01 pH unit, add next titrant, while being titrated to pH value 3, stop, after balance 2 hours, then be 9 by the slow volumetric soiutions of NaOH to the pH value of 0.02M, balance criterion is that pH fluctuation in every 60 seconds is less than 0.01 unit.General whole titration process roughly needs 15 to 20 hours.Record the pH value of titration point and add soda acid volume.Add the total proton concentration in system to be:

$\mathrm{TOTH}=\frac{C_a{V}_a-C_b{V}_b}{V_0+V_a+V_b}---\left(8\right)$

Wherein: TOTH: total proton concentration (M) in system, C _aand C _bthe concentration (M) of bronsted lowry acids and bases bronsted lowry in titration process, V _ato add sour cumulative volume (L), V _beach volume that is added dropwise to alkali (L), V ₀it is the initial soln volume (L) of suspension system.

Extension rate D in system is:

$D=\frac{V_0+V_a}{V_0+V_a+V_b}---\left(9\right)$

Titration curve data substitution nonlinear optimization program FITEQL 3.1 (Westall, 1994) are calculated, and FITEQL is an iterative optimization procedure, can go out equilibrium constant value logK according to input data fitting ₍₊₎, logK _(-)and logK _{(Na, H)}, and κ.FITEQL characterizes the quality of fitting result by this value of WSOS/DF, general WSOS/DF value, between 0.1～20, thinks that fitting result is better.

Adopt as in Figure 2-4 automatic potentiometric titration to measure three kinds of soil clay minerals at 0.1M, 0.01M and 0.001MNaNO ₃back-ground electolyte condition under titration curve, in figure, represent the acid adding amount under different ionic strength condition, lines are that FITEQL ver3.1 is according to the fitting result of table 4 (Sd=4g/l).Application FITEQL ver3.1 carrys out matching clay Potentiometric Data, obtains clay mineral surface acid base constant: log K ₍₊₎, log K _(-)and logK _{(Na, H)}(in table 4).

The 3rd step batch adsorption experiment method is measured the metal surface complex reaction constant on clay mineral surface:

Take 25 parts of 0.04g soil clay minerals, be placed in respectively 50mL centrifuge tube, respectively add 10mL0.01molL ^-1naNO ₃, then add respectively a certain amount of 0.1molL ^-1hNO ₃or 0.02molL ^-1naOH regulates pH, then adds separately the Pb of 1000mg/L ²⁺the each 50 μ L of stock solution, finally adding appropriate ultrapure water to make the volume of suspension in each centrifuge tube is 10.25mL.After jumping a queue, under 25 DEG C of conditions, vibrate 3 days, then centrifuge tube is placed in to the centrifugal 20min of rotating speed with 7500rpm on supercentrifuge, with 0.22 μ m nylon leaching film filtration, the Pb in filtrate ²⁺ion concentration is measured with atomic absorption spectrophotometer (AAS).Pb ²⁺adsorbance deduct concentration in supernatant by addition and calculate gained.The blank test of absorption is except not adding clay mineral, and other operations are the same respectively.Adsorpting data adopts FITEQL ver.3.1 to simulate the metal surface complex reaction constant value logK of Pb on soil clay mineral surface _(AlOPb)and logK _(X2Pb)." II.Species " stoichiometry matrix relationship used in FITEQL is in table 3.

Table 3.Pb (II) adsorbs the stoichiometric relationship table of " II.Species " in FITEQL on clay mineral

Adopt batch adsorption experiment, obtain in titration experiments on the basis of mineral surface soda acid constant value (table 4), the metal surface complex reaction constant value logK of Pb on three kinds of soil clay mineral surfaces that adopted FITEQL ver.3.1 matching _(AlOPb)and logK _(X2Pb)(in table 4).Model to the adsorption curve fitting result of metallic ion see Fig. 5-7 and, for Pb wherein, in the absorption behavior on three kinds of soil clay mineral surfaces and models fitting result, (wherein ordinate is Pb absorption number percent, solid line in Fig. 5-7, dotted line, dotted line represents respectively I=0.001M, 0.01M, the fitting result under 0.1M, square, circle, triangle represents I=0.001M, 0.01M, experimental data under 0.1M, back-ground electolyte is NaNO ₃, Sd=4g/l).

Table 4-Pb is in the Surface Complexation Model parameter on three kinds of soil clay mineral surfaces

A: the CEC value difference value when CEC value when point bit density of ≡ SOH is pH=8 and pH=4,

B: the CEC value when point bit density of ≡ X-H is pH=4

C: by FITEQL Optimal Fitting

D: by N ₂-BET method records

The 4th step builds full soil model (taking Red Soil as example, Nanjing yellowish soil, the same Red Soil of Heilungkiang black earth implementation step)

For research soil, measure soil parameters, comprising: soil pH value, soil organic matter content OM%, the soil texture, soil clay mineral content clay%, soil ferriferous oxide content F e ₂o ₃hNO when % and pH=2 ₃extract Pb concentration in soil, and the CEC value of the mineral of measuring in above-mentioned steps and specific surface area S _sthe metal surface complex reaction constant on the soda acid constant value on clay mineral surface and clay mineral surface, according to Pb at the adsorption reaction on ferriferous oxide surface and Pb the adsorption reaction relation on organic surface, from document, Pb (II) adopts permanent capacitor C CM model on soil ferriferous oxide goethite surface, and at the organic surperficial electrostatic double layer BSM model that adopts two point position, corresponding reaction constant and model parameter are in table 5

Table 5Pb (II) is in SCM model and the corresponding reaction constant value on goethite and organic surface

a：Gunneriusson，L.， L.& S.1994，Complexation of Pb(II) at the goethite(α-FeOOH)/water interface，Geochimica et Cosmochimica Acta.58，22，p.4973-4983

b：Liu，AG.and Gonzalez，R.D.，2000，Modeling adsorption of Copper(II)，Cadmium(II)and Lead(II) onpurified humic acid，Langmuir，16，3902-3909

The adsorption reaction on organic surface at the adsorption reaction on ferriferous oxide surface and Pb according to Pb, search the equilibrium constant value of Pb in solution in document, SCM model in conjunction with Pb on the each solid phase components of soil, create the stoichiometry matrix table (in table 6) that in soil, Pb form is calculated and build full soil model, this matrix is laterally the mass action system of equations that geochemical balance model needs, and keeps weighing apparatus system of equations and be longitudinally quality.

According to the stoichiometry matrix table of table 6, the concentration of each form when help that can computer calculates balance, thus obtain the ADSORPTION STATE concentration of Pb at the soil liquid and each solid phase surface.

By the stoichiometry matrix of the surface complexation constant substitution table 6 in table 4, can obtain the stoichiometry matrix relationship under complete native condition.Can obtain content and each adsorption site site concentration value and the specific surface area of each solid phase component according to table 2, from table 5 and table 4, can obtain and calculate other required parameters, as κ.Computer, can calculate the concentration value of all chemical forms in table 6.The model calculation Pb adsorption experiment and the comparison of computational results on three kinds of soil under different pH condition as shown in Fig. 8-10 of comparing with adsorption experiment result, round dot is experimental data, solid line is result of calculation (I=0.01M NaNO ₃), result demonstration, the model calculation and Comparison of experiment results coincide, and illustrate that the method has feasibility.

Claims (2)

1. a definite method for Pb (II) solubilised state and ADSORPTION STATE in mineral soil, comprises the following steps:

The first step: separate soil clay mineral, measure CEC value and the specific surface area S of mineral _s:

1) acetic acid/sodium acetate buffer solution removal carbonate;

2) sodium hydrosulfite is removed ferriferous oxide;

3) hydrogen peroxide is removed organic;

4) sedimentation is collected the soil clay mineral of <2 μ m;

5) adopt dialysis pickling, Na ion saturated mineral surface;

6) measure the cation exchange capacity (CEC) CEC value under pH=4 and pH=8 condition, N ₂-BET method is measured mineral

Specific surface area S _s;

Second step: the soda acid constant value logK on potentiometric determination clay mineral surface ₍₊₎, logK _(-)and logK _{(Na, H)}:

Adopt two point position method, clay mineral is divided into two some positions to the absorption of Pb (II): the permanent negative charge ≡ X of the variable charge ≡ AlOH at mineral edge and interlayer ^-, adopt the electrostatic attraction on permanent capacitor C CM models fitting surface, adopt automatical potentiometric titrimeter and back titration method to obtain the titration curve of clay mineral, substitution nonlinear optimization program FITEQL ver3.1 carries out matching and measures the soda acid constant value logK on clay mineral surface ₍₊₎, logK _(-)and logK _{(Na, H)};

The 3rd step: batch adsorption experiment method is measured the metal surface complex reaction constant logK on clay mineral surface _(AlOPb)and logK _(X2Pb);

The 4th step: measure the weight percent content of organic matter, ferriferous oxide and the clay mineral of soil, build full soil model:

For research soil, measure soil parameters, comprising: soil pH value, soil organic matter content OM%, the soil texture, soil clay mineral content clay%, soil ferriferous oxide content F e ₂o ₃hNO when % and pH=2 ₃extract Pb (II) concentration in soil, and the CEC value of the mineral of measuring in above-mentioned steps and specific surface area S _s, the metal surface complex reaction constant on the soda acid constant value on clay mineral surface and clay mineral surface, according to Pb at the adsorption reaction on ferriferous oxide surface and Pb (II) the adsorption reaction relation on organic surface, search the equilibrium constant value of Pb in document (II) in solution, SCM model in conjunction with Pb (II) on the each solid phase components of soil, create the stoichiometry matrix table that in soil, Pb (II) form is calculated, build full soil model, matrix is laterally the mass action system of equations that geochemical balance model needs, keep weighing apparatus system of equations and be longitudinally quality, according to document and experimental result, each solid phase adsorption point site concentration Ns is respectively:

Clay mineral:

Ns _(≡AlOH)＝M％S _d*(CEC ₈-CEC ₄)*10 ^-5

Ns _(≡X-.H+)＝M％S _d*CEC ₄*10 ^-5

Ferriferous oxide:

Ns _(≡FeOH)＝M％Sd*13.56*10 ^-5

The soil organism:

Ns _(≡S1)＝M％S _d*255*10 ^-5

Ns _(≡S2)＝M％S _d*63*10 ^-5

According to stoichiometry matrix table, the concentration of each form when help that can computer calculates balance, thus obtain the ADSORPTION STATE concentration of Pb (II) at the soil liquid and each solid phase surface.

2. definite method of Pb (II) solubilised state and ADSORPTION STATE in mineral soil according to claim 1, it is characterized in that, described the 3rd step adopts batch adsorption experiment method to measure the adsorption curve under different pH values or ionic strength conditions, and substitution FITEQL ver3.1 simulates the metal surface complex reaction constant value logK of Pb (II) on soil clay mineral surface _(AlOPb)and logK _(X2Pb).