Determination method of Feed montmorillonite Ammonium exchange capacity

Theory：　

Heat sample with NH4CL solution, make NH4+ adsorbed completely by montmorillonite, because ions K+ and NH4+ are easy to be changed by montmorillonite, so wash sample by KCL solution, NH4+ is exchanged, NH4+(ka<10-3) is a kind of very weak acid, it can not be dropped by alkali directly, add formaldehyde to make NH4+ and formaldehyde react six methylene four amino acid and quantitative strong acid, so drop sodium hydroxide solution, use phenolphthalein as director, each ion reaction is as follows:

　R—NH4++K+R—K++ NH4+

　4NH4++6HCHO=（CH2）6N4H++3H++6H2O

　4OH—+（CH2）6N4H++3H+=（CH2）6N4+4H2O

Reagent and solution：

　　0.1000mol/L of NaOH standard solution,using Potassium hydrogen phthalate calibration  

　　1mol/L NH4CL solution,weigh NH4CL53.5gto put it into 1000mLbeaker, dissolve without water, dilute to 1000mL.

　　1mol/LKCl solution：weigh KCl74.5gto put it into 1000mL beaker, dissolve with water, dilute to 1000ml.

　　Neural formaldehyde, take 37% formaldehyde 50ml, add phenolphthalein two drops, above NaOH drop to appear light red.

　　1%AgNO3solution,take0.1gAgNO3solube into 1ml water.

　　1%phenolphthalein director, take 0.5g phenolphthalein, dissolve it into 50ml 95% ethanol.

Determination procedure：

Weigh sample with 80 meshes 1g(correct to 0.0002g) to 300ml beaker, use measuring cylinder measure 100ml NH4CL solution into beaker, put the beaker on the oven with thermal control to heat up to boil, keep boiling 1h, stirring with glass rob every few minutes, properly add water, remove the beaker, cool it to room temperature, filter with middle speed filter paper,  use distilled water to wash sample, until no chloride ion(use 1% AgNO3 to test filter solution, no obvious turbidity), at last, remove all sample to filter paper, move the filtrate, change 250ml conical flask to receive it, use hot KCL solution with the principle of a small amount many times to wash sample in funnel completely, wash it to 100ml of total volume, add 10ml neutral formaldehyde, place 5min, add phenolphthalein two drops, drop NaOH standard solution to light red, 30s fastness, write down consumed volume of NaOH, at the same time, do blank experiment.  

Result calculation：

　　Ammonium exchange volume（m mol/100g）= C×(v1-v2) /w ×100

　　In Formulate：C——amount of NaOH standard solution concentration substance, mol/L；

　　V1——consumed NaOH volume during dropping, mL;

　　W——sample weight, g；

V2——test consumed NaOH volume in blank experiment, mL.

Cautions：

 Formaldehyde due to air oxidation, often contains a small amount of formic acid, should be neutralized with NaOH, or will deviate from the measurement results

The end of dropping, produced (CH2)6N4 is a kind of organic weak base( kb=4×10－9, after calculation, PH value is about 8.5 in theory), so color in the end change colorless to light red. 　

Reaction between Formaldehyde and NH4+in room temperature go slower, after adding formaldehyde and place few minutes to make it react completely.

Wash sample at the first time, it should be gone in beaker, it is easy to clean up chloride ion, and avoiding thin montmorillonite from plugging up the Filter hole, and affect the filtering speed.