Preparation And Characterization Of Montmorillonite Powder With High Purity

Bentonite clays consisting mainly of montmorillonite are utilized in various engineering applications. Bentonite is a good adsorbent, which can absorb harmful and noxious substances, and can be used as a remedy for infections, indigestion, and other medical problems both by applying wet clay topically to the skin as a poultice and by ingesting it. Bentonite can be used as additive in cosmetics and as a clarifying agent for wine clarification. However, natural bentonites contain many kinds of impurities such as quartz,α-cristobalite, feldspar, zeolite, calcite etc., which can decrease performance of the bentonite. Furthermore, quartz andα-cristobalite are carcinogenic. Therefore purification of removal of the impurities in bentonite is critical to its applications. It is necessary that purify the bentonite before using it. Of all impurities, it is most difficult to get rid of theα-cristobalite from the bentonite, because of its tiny particles.Primary studies indicated thatα-cristobalite was the major impurity of the bentonite from Jianping, Liaoning and Ningcheng, Inner Mongolia, so some samples were chosen from this area.Size fractions under 2μm were separated from the bulk samples by sedimentation method. Mineral composition analysis showed that the impurities including quartz, feldspar and zeolite had been removed by this method, but theα-cristobalite also existed. TEM observation indicated that particles ofα-cristobalite were thinner than that of montmorillonite, soα-cristobalite could not be removed from bentonite though the physical methods.In this paper,α-cristobalite was removed from bentonite clays after NaOH treatment. Optimum reaction conditions were obtained: oscillated under water bath, temperature 60℃for 2 hour, liquid-solid ratio 10mL/1g, the concentration of NaOH solution y = 4.84x + 0.5007(mol/L), R2 = 0.9864, where x as content ofα-cristobalite in bentonite.The centrifuged supernatant after NaOH treatment was dried and analyzed. Results showed that main phase was sodium metasilicate, with minor amount of sodium carbonate. Chemical analysis indicated that only Si inα-cristobalite was dissolved, Al in montmorillonite was not dissolved. Combined with XRD analysis of alkali-treated bentonite, structure of montmorillonite was not destroyed.The processing condition for preparing montmorillonite with high purity was designed, and costing calculation was carried out. Compared with market price, the cost for preparing montmorillonite with high purity was much cheaper. Water is recycled, and sodium metasilicate solution can be used as sodium modifier.