Determination of the cation exchange capacity of montmorillonite

Provided by HZM Group

There are many ways to test CEC, such as nitrogen distillation method,  ammonium acetate method, ammonium chloride - sodium acetate method, chloride - ethanol method, chloride - ammonia method, barium - sulfuric acid methodetc. So far, CEC detection of montmorillonite depends on National standard JC/T 593—1995.

(montmorillonite test methods), detailed methods are as following:

　　（1）Method summary

Dealing with montmorillonite samples with extracting agent containing instruction cation NH4+, replace exchangable cation of samples in extracting solution, make sample adsorption cation instructions convert into ammonium. Seperate ammonium base soil with extracting solution, test potassium, sodium, calcium and magnesium ions in extracting solution, that is the corresponding amount of exchangeable cations

（2）Main reagents and material

a. Centrifuge：Measuring range 0～400r/min；

b. Magnetic stirrer：Measuring range 50～2 400r/min'

c. Potassium, sodium, calcium, magnesium mixed standard solution〔c(0.01Na+、0.005Ca2+、0.005Mg2+、0.002K+)〕weigh 0.5004g Calcium Carbonate(Reference reagents)，0.201 5gMagnesia(Reference reagents)，0.5844g Sodium chloride(Purity reagents)和0.1491g Potassium chloride(Purity reagents) into 250mL beaker, after adding water to a small amount of dilute hydrochloric acid to dissolve (be careful to prevent jumping splash)。Heatedup to boiling and rush to make carbon dioxide, cooling. Remove solution to 1000ml flask, dilute with water to mark, shake well, move it in a dry plastic bottle and save

d. Exchange fluids：weigh 28.6g Ammonium chloride to 250ml water, add 600ml Ethanol, shake well, using 1+1 Ammonia water to adjust PH to 8.2, dislute with water to 1L, that is 0.5mol/L -60% Ammonium chloride Ethanol solution.

e. EDTA standard solution〔c(0.01EDTA)〕：take 3.72g Disodium ethylenediaminetetraacetate to dissolve it to 1000ml water.

Demarcate: Draw 10mL0.01mol/L Calcium chloride(Reference reagents) standard solution into 100ml beaker, dislute with water to 40~50ml. Adding 5ml 4mol/L Sodium hydroxide solution, make PH to be 12~13, add a little acid chrome blue K- naphthol green B mixed indicator, use EDTA solution to pure blue as the end.

c1= c2?V3/ V4

In formula：

c1——The actual concentration of EDTA standard solution, mol/L；

c2——Standard solution of calcium chloride，mol/L；

V3——Volume of standard solution of calcium chloride，mL；

V4——Volume of consumed EDTA titration standard solution during dropping，mL

f. Washing liquid：50% Ethanol，95% Ethanol。

（3）Test procedure

　　Weigh 1.000g sample to dry at 115~110 degree, place it in 100mL centrifuge tube. Add 20mL50% ethanol, stirring 3 ~ 5min on a magnetic stirrer and remove it, after centrifugation (rotational speed of about 300r / min), discard supernatant in tube, and add 50ml Exchange fluids in Centrifuge tube, after stirring 30 mins on a magnetic stirrerand removed, centrifuged, the supernatant was collected to 100mL flask. The residue and the inner wall of the tube was washed with 95% ethanol (about 20mL), after stirring and centrifuged, the supernatant were combined in the above 100mL flask, dislute with water to the mark, shake well, preparing to test. The residue was removed.

Determination of exchangeable calcium and magnesium, take the above liquor 25mL, put it in 150ml beaker, dilute with water to 50ml, add 1ml 1+1 triethanolamine and 3 ~ 4mL4mol / L sodium hydroxide, add a little acid chrome blue K- naphthol green B mixed indicator, drop 0.01mol/LEDTA standard solution to pure blue, write down the reading V5, then use 1+1 Hydrochloric acid Neutralized to pH 7, then add ammonia - ammonium chloride buffer solution (pH = 10), then 0.01mol / LEDTA standard solution dropwise to pure blue note the reading V6.

Determination of exchangeable potassium, sodium: take 25ml solution into 100ml beaker, add 2~3 droplets 1+1 Hydrochloric acid, dry it with low temperature. Add 1ml 1+1 hydrochloric and 15~20ml water, Micro thermal dissolution of soluble salts, cooled it and removed the solution to 100ml flask, diluted with water to mark, shake well, determinated potassium and sodium in the flame photometer. The standard curve: seperately take 0,3,6,9,12,15ml potassium, sodium, calcium, magnesium mixed standard solution to 100ml flask, add 2ml 1+1 hydrochloric, diluted with water to mark, shake well. Measured  the reading of sodium and potassium under the same conditions, and draw the standard curve(this standard series correspond to contain exchangeable sodium of 0、170、345、520、690、860mg  and exchangeable potassium of 0、60、120、175、240、295mg in each 100g sample.

（4）Calculated results

　Calcium and magnesium are calculated as follows:

　Exchangeable calcium g/100g= （40c5V5）/（2.5m3）

　Exchangeable Mg g/100g=[ 24c5(V6-V5)]/ （2.5m3）

In formula：

c5—EDTA actual Molar concentration of standard solution mol/L；

V6、V5—Consumed Milliliters of EDTA standard solution during dropping,mL；

m3——sample quality, g

Content of potassium and sodium, calculated by formula 10

Exchangable potassium(g/100g)= Kmg /（2.5m3）

Exchangable sodium (g/100g)= Namg/（2.5m3）

In formula：

Kmg，Namg—Checked milliters of potassium and sodium by standard curve;

m3——sample quality，g