Modified Bentonite Absorbent Preparation And Application In Wastewater Treatment

Bentonite is a clay mineral with expandable layer structure that primary constituent of montmorillonite. Modification of bentonite results in a net permanent charge, therefore it has the reversible cantion exchange capability and very plastic properties.Modified bentonite can be prepared by introducing gallery templates, such as simple metal cations, quaternary ammoniumcanons, long chain amines, and hydroxyed inorganic metal ions. Thus formed modified-bentonite have improved capabilities to adsorb hydrophobic contaminants and are widely used as sorbents to treat industrial wastewaters. They also have a lot of applications in other various areas.This dissertation first gives a comprehensive review, which is on the recent progress in the research and development on the modifying and applications of bentonites. Special attention is paid to the modifying of bentonites with hydrated polymeric inorganic cantions, such as A1. With greatly improved sorption property, surface acidity and thermal stability, modified possess great promise to be used as catalysts and adsorbents, especially far environmental protection and pollution control applications.Because the bentonite content of natural bentonite clay is usually low, the methods of purification and ion exchanging of raw bentonite with NaCl into Na-bentonite are described and investigated. The procedure and conditions are optimized. It is found that (NaPO₃)₆ solution is the best dispersing agent for the purification of bentonite. The optimum concentration of (NaPO₃)₆ solution is about 0.15 wt% with the pH value of 7.0. When the raw bentonite is ion exchanged with NaCl, the optimum concentration of NaCl is about 1.0 mol/L with the Ph value of 5.0-6.0. The data of XRD, F-XRD and other chemical analysis shows that the content of montmorillonite in the above-treated bentonite increased to more than 90%. The spacing distance (d(001))value of Na- bentonite reduces to 12.73 A indicating that Ca-bentonite has been successfully converted to Na-form.Recently, the modified bentoniteswere prepared based on Al-pillared bentonites (Al-Bentonite).Therefore it was important to study it's preparation and the factors deeply. By means of AlCl₃ hydrolyzing in NaOH solution, the author prepared Al-Bentonites which were characterized by XRD, XRF, FT-IR, SEM etc. Some factors in the experiments were studied in detail. The result showed that theconcentration of AICI3, NaOH, Al-modifying solution didn't affect the basal spacing and thermal stability of Al-Bentonites greatly. The high OH/A1 ratio and large amounts of Al-modifying solution favored the basal spacing and thermal stability of Al-Bentonites. The surface area would declined if 0H/A1 ratio was too high or the amounts of Al-modifying solution was too much. The aging of Al-modifying solution at higher temperature improved the basal spacing and thermal stability, surface area and pore volumes of Al-Bentonites. However the properties of Al-Bentonites were independent of the adding order between the bentonite solution and the Al-modifying solution.Based on the above experiments, the author studied the mixed metallic modified bentonites. The experimental result indicated that the microporous structure of Fe-Al-Bentonites was affected by the changing of interlayer Fe-Al polymer with different Fe/Al ratio. But the presence of Al iron was helpful to incorporate Fe iron into interlayer of bentonites. The surface area and pore volumes of Al-Bentonites increased mainly because of increasing the external surface area and mesoporous volumes after acid-activating. This conclusion confirmed that the microporous structure of modifying clay depends upon the interlayer modifyer.The applications of above-made modified bentonites, especially A1-, Fe-Al- > Al-acid-bentonites, in environmental protection and pollution control has been investigated. The adsorption experiments using phenol show that Al- n Fe-Al- -. Al-acid-bentonites are all good adsorbents to treat organic wastewater, even better than Na- bentonite. The pH value of the solutions has great effect on the removal percentage of the phenol by these hydroxy-metal modified bentonites. For example, almost 99.6% of phenol can be adsorbed and removed by Al- bentonite, when pH value of the solution is about 10.0 as compared to that only about 50% of that phenol can be removed when pH value is about 2.0. The adsorption mechanism of phenol on the modified bentonites has also been proposed. After incandescing at 500 °C modified bentonite can use recycle. The phenol sorption characteristic of Al modified bentonite is researched. The results show that immoilized modified bentonite has a strong sorption capability for phenol. Temperature has little influence on the adsorption of phenol. The adsorption of phenol is greatly affected by the iitial phenol concentration, the flow speed of phenol solution and regeneration reagent.