HJ 746-2015Soil. Determination of redov potential. Potential method (English PDF)

Foreword

To carry out the "People's Republic of China Environmental Protection Law" to protect the environment, protect human health, regulate soil oxidation and reduction potential of the test Set this standard.

This standard specifies the field test method for the determination of redox potential in soils.

This standard is modified using the "Field Test Method for Determination of Reducing Potentials of Soil Mass" (ISO 11271.:2002).

The main changes are as follows.

- modified standard name;

- the original reference standard ISO 3696. 1987 to GB/T 6682;

- simplifies the formulation of the principle of the method;

- refinement of instruments and equipment terms;

- modified the analysis steps;

- Added caution.

This standard is the first release.

Appendix A to this standard is a normative appendix, Appendix B and Appendix C are informative appendices.

This standard is organized by the Ministry of Environmental Protection Science and Technology Standards Division.

The main drafting unit of this standard. Jinzhou City Environmental Monitoring Center Station.

This standard is approved by the Ministry of Environmental Protection on June 4, 2015.

This standard is implemented as of July 1, 2015.

This standard is explained by the Ministry of Environmental Protection.

Determination of soil oxidation - reduction potential

1 Scope of application

This standard specifies the soil oxidation-reduction potential of the field test method.

This standard applies to the determination of the redox potential of fresh or moist soils given in Annex A for the water state.

2 Normative reference documents

The contents of this standard refer to the following documents or their terms. For undated references, the valid version applies to this standard quasi.

GB/T 6682 Analytical laboratory water specifications and test methods Technical specification for soil environmental monitoring ISO 11271.:2002 Determination of soil mass oxidation and reduction potential Field test method (Soil quality-Determination of redox Potential-field method

3 Terms and definitions

The following terms and definitions apply to this standard.

Soil Oxidation - Reduction Potential EhSoil Redoxpotential Refers to the soil oxidation state substances and the reduction of the relative concentration of substances generated by the potential, expressed by Eh.

4 Principle of the method

The platinum electrode and the reference electrode are inserted into fresh or moist soil, and the soluble oxidant or reducing agent in the soil is accepted from the platinum electrode or give electrons until a potential is established on the surface of the electrode to measure the difference between the potential and the potential of the reference electrode, the electrode is added to the potential of the hydrogen standard electrode to obtain the redox potential of the soil.

5 Reagents and materials

Unless otherwise stated, analytical pure chemical reagents conforming to national standards are used in the analysis, and the test water meets the requirements of GB/T 6682.

5.1 quinone hydroquinone (C12H10O4).

5.2 potassium ferricyanide (K3 [Fe (CN) 6]).

5.3 Potassium ferrocyanide (K4Fe (CN) 6 · 3H2O).

5.4 agar. omega = 0.5%.

5.5 Potassium chloride. KCl.

5.6 Redox Buffer Solution.

Adding the appropriate amount of powdered quinone hydroquinone (5.1) to the pH buffer to obtain a suspension; or equimolar potassium ferricyanide (5.2) Potassium cyanide (5.3) (mol/mol). Refer to Appendix B for the potential values of the standard redox buffer solution.

5.7 Potassium chloride solution. c (KCl) = 1.00 mol/L.

Weigh 74.55 g potassium chloride (5.5) in 1000 ml volumetric flask, diluted with water to the mark, mix.

5.8 Potassium chloride solution. c (KCl) = 3.00 mol/L.

Weigh 223.65 g potassium chloride (5.5) in 1000 ml volumetric flask, diluted with water to the mark, mix.

5.9 Electrode cleaning materials. fine sandpaper, decontamination powder, cotton cloth.

6 Instruments and equipment

6.1 potentiometer. input impedance of not less than 10 Gohm, sensitivity of 1 mV.

6.2 Redox electrode. Platinum electrode, need to be stored in the air and keep clean. The structure of the two different types of platinum electrodes is shown in Fig.

A) redox electrode b) spike redox electrode 1 insulating material; 2 copper rod; 3 platinum wire; 4 handle; 5 jack; 6 steel rod; 7 epoxy resin; 8 exposed platinum wire bundle Fig.1 Structure of redox electrode

6.3 Reference electrode.

Silver-silver chloride electrode, other electrodes such as calomel electrodes can also be used. The potential of the reference electrode relative to the standard hydrogen electrode is given in the Appendix C. Silver-silver chloride electrode should be stored in 1.00 mol/L or 3.00 mol/L potassium chloride solution (5.7 or 5.8), the concentration of potassium chloride and the electrodes are of the same concentration or are stored directly in a salt bridge containing the same concentration of potassium chloride solution.

6.4 stainless steel hollow rod. diameter greater than the redox electrode 2 mm, the length should meet the redox electrode inserted into the soil required depth.

6.5 salt bridge. connecting the reference electrode and soil, salt bridge structure shown in Figure 2.

1 silver-silver chloride electrode; 2 agar potassium chloride solution (omega = 0.5%); 3 ceramic sleeve Fig.2 Salt bridge structure in redox potential measurement

6.6 Hand drill. diameter greater than the salt bridge reference electrode 3 mm ~ 5 mm.

6.7 Thermometer. Sensitivity ± 1 °C.

7 Scene

According to the relevant requirements of HJ/T 166, according to the background data and field investigation results, the spatial diversity of pollutants and the degree of soil pollution the basic judgment selects the measurement site. In the selected measurement point, should be removed rubble, gravel and other large particles of impurities.

8 Analysis steps

9 Results calculation and representation

10 Precautions

10.1 The use of the same platinum electrode continuous testing of different types of soil, the instrument readings often lag phenomenon, this time should be measured in each After the sample is measured, the electrode is cleaned and cleaned. If necessary, the electrode is placed in saturated KCl solution soak, until the reference electrode to restore the original state can be used.

10.2 If the soil moisture content is less than 5%, the distance between the platinum electrode and the reference electrode should be minimized to reduce the resistance in the circuit.

10.3 Platinum electrodes are used within one year and check whether the platinum electrodes are damaged or contaminated before each use. If the platinum electrode is contaminated, it is available Wipe the cotton cloth and rinse it with distilled water.

10.4 Platinum Electrode Before use, apply the redox buffer solution (5.6) to check its response value if its measured potential value is proportional to the oxidation reduction the difference between the potential values of the solution (5.6) is greater than 10 mV and should be purged or replaced. Also check the reference electrode. Reference electrode available to detect each other, but at least three reference electrodes need to be connected in turns, when the reading of an electrode and other electrodes read the difference of more than 10 MV, the electrode can be regarded as defective and should be discarded.

Appendix A

(Normative appendix) Evaluation of soil water status

Table A Soil water status assessment

Soil identification soil evaluation nature > 17% clay Appendix B (Informative) Standard redox buffer solution potential value

Table B.1 Standard Oxidation Reduction Buffer Solution Potential (quinone hydroquinone)

PH = 4 (mV) pH = 7 (mV) Reference electrode 20 ° C 25 ° C 30 ° C 20 ° C 25 ° C 30 ° C Saturated silver - chloride 268 263 258 92 86 79 Saturated calomel electrode 223 218 213 47 41 34 Saturated hydrogen electrode 471 462 454 295 285 275

Table B.2 Standard oxidation-reduction buffer solution potential (potassium ferricyanide-potassium ferrocyanide)

PH Eh (mV) pH Eh (mV) 2 750 10 -150 3 710 11 -320 4 620 12 -480 5 500 13 -560 6 390 14 -620

Table B.3 Standard Redox Buffer Solution Potential Values (Standard Hydrogen Electrode)

Mol/L Eh (mV)

0.01 415

0.007 409

0.004 401

0.002 391

0.001 383

Note. with 0.001 mol/L potassium ferricyanide and potassium ferrocyanide solution measured the most accurate.

A potassium ferricyanide and potassium ferrocyanide solution concentrations are equal.

Appendix C

(Informative)

Reference electrode potential value

Table C Potential value of the reference electrode corresponding to the standard hydrogen electrode at different temperatures Unit. mV

Calomel electrode

0.1mol/L KCl

Calomel electrode

1mol/L KCl

Calomel electrode

Saturated KCl

Silver - chloride 1mol/L KCl Silver - chloride 3mol/L KCl Silver - chloride Saturated KCl 50 331 274 227 221 188 174 45 333 273 231 224 192 182 40 335 275 234 227 196 186 35 335 277 238 230.200 191 30 335 280 241 233 203 194 25 336 283 244 236 205 198 20 336 284 248 239 211 202 15 336 286 251 242 214 207 10 336 287 254 244 217 211 5 335 285 257 247 221 219 0 337 288 260 249 224 222