Study On Sodium-modified And Reusability Of Foundry Ca-bentonite

As an important clay mineral, bentonite is widely used and increasingly demanded in industries such as casting, metallurgy, drilling, petrochemical and papermaking. Bentonite has a large number of reserves in China. However, the majority of natural bentonite is Ca-bentonite, which has low grade and poor quality, and needs further processing for application. As Na-bentonite has better strength, expansion, bonding, and thermal stability than Ca-bentonite, it has wide application in casting as a foundry binder and has also become the largest user of foundry industry in which more than one million tons are used each year. For this reason, it's significant to investigate the sodium-modified process of Ca-bentonite.In this study, two Ca-bentonite of different grade, used as the original soil for modification, are produced from different grade of ore occurrence in Hubei, and their montmorillonite content are 93.2% and 82.6%. For the modified process is semi-dry process, our experiment focused on sodium agent powder adding method and sodium agent solution adding method in the method of adding sodium agent. In the orthogonal experiment, we select four influencing factors and their corresponding factors: water content, sodium agent content, storage time and the squeeze numbers, and swelling value, green compressive strength was used as the performance indicators to compare the two modified methods. Through mathematical analysis, the best formula and process were expected.The swelling volume, swelling value and green compressive strength of modified bentonite showed that the sodium agent solution adding method is superior to sodium agent powder adding method. The reusability of modified bentonite was compared by measuring methylene blue adsorption and green compressive strength. These results showed that the hydration characteristics and reusability of modified bentonite can meet the requirement of casting production.Modified sodium bentonite can improve the reusability, and the preliminary study on the mechanism of this by X-ray diffraction and differential thermal analysis showed that sodium ions strengthen the crystal structure after entering the bentonite unit inter-layer, which obviously improved the reusability after modified.