Experimental study on sodium modification and purification of GMZ bentonite

Na-bentonite of high purity has numerous applications in many industries. The raw bentonite ore contains many impurities and consists mainly of Ca-bentonite. In this study, sodium chloride (NaCl), sodium carbonate (Na2CO3), sodium pyrophosphate (Na4P2O7), and sodium hexametaphosphate (NaPO3)6 were used to modify GMZ bentonite, followed by purification. The optimal modification and purification conditions (such as inorganic salt, temperature, time, dosage, and particle size) were determined by testing the montmorillonite content, adsorption and expansion properties of modified bentonite. The results showed that the modification effect was the best when NaCl was added at t = 3 h and T = 60 °C. During the modification process, Na+ replaced Ca2+ and Mg2+ through ion exchange; the impurity minerals, quartz and feldspar, were removed from the bentonite by purification; and the montmorillonite content increases from 46.6 % to around 90 %. The modification effects of NaCl, Na4P2O7, and (NaPO3)6 were improved with the dosage increasing, and Na2CO3 can complete the modification of GMZ bentonite when the dosage was 2 %. Compared with the bentonite purified by tap water (TW) and deionized water (DW), the yield of bentonite can be greatly improved by adopting the technique of modifying first and then purifying.