Adsorption of hexavalent chromium onto kaolin clay based adsorbent

A low-cost adsorbent modified kaolin clay(MKC) was synthesized and utilized for Cr(VI) removal from aqueous solution. Adsorption experiments were carried out as a function of adsorbent dosage, solution pH, Cr(VI) mass concentration, contact time, electrolyte, and temperature. It is found that the adsorption efficiency is high within a wide pH range of 2.5-11.5, and equilibrium is achieved within 180 min. Increases in temperature and electrolyte concentration decrease the adsorption. The adsorption follows the pseudo-second-order kinetic model. The Langmuir isotherm shows better fit than Freundlich isotherm. The maximum uptake capacities calculated from the Langmuir model are 15.82, 15.55 and 15.22 mg/g at 298, 308 and 318 K, respectively. Thermodynamic parameters reveals the spontaneous and exothermic nature of the adsorption. The FTIR study indicates that hydroxyl groups, NH4+ ions and NO3- ions on MKC surface play a key role in Cr(VI) adsorption. The Cr(VI) desorbability of 86.53% is achieved at a Na2CO3 solution. The results show that MKC is suitable as a low-cost adsorbent for Cr(VI) removal which has higher adsorption capacity and faster adsorption rate at pH close to that where pollutants are usually found in the environment.

Eco-friendly PVA/Kaolin Clay Coating for Barrier Paper

The resistance of wood-fiber paper to water, grease, and water vapor is usually attained by immersing the base paper in hydrophobic oil, laminating with a plastic or metal film, or the application of a barrier coating. Oil impregnation and the addition of films may make the paper difficult to recycle or persistent in the environment owing to their strong binding force and nondegradability. Environmental concerns have attracted worldwide attention to eco-friendly barrier coatings. In this study, degradable polyvinyl alcohol(PVA) and kaolin clay pigment were used to prepare coatings that were applied to a base paper. By measuring the barrier properties of the coated paper, including the water absorptiveness(Cobb60 value), Hercules sizing degree, oil resistance(Kit rating), and water vapor transmission rate(WVTR), an optimal coating formulation and process were proposed. To examine the barrier mechanism of the PVA/kaolin clay coating, we characterized the coating microstructures using a scanning electron microscopy(SEM) and a mercury porosimeter. The results showed that the Cobb60 value and water vapor transmission rate of the coated paper decreased by 61.4% and 98.6%, respectively, compared with the base paper, for a pre-coating weight of 0.98 g/m^2 and a top-coating weight of about 3.23 g/m^2. Furthermore, the Hercules sizing degree rose by a factor of 337.2, while the oil resistance(Kit rating) increased from 0 to 12. The optimum drying temperature for a wet coating layer was found to be 170℃, and the optimum weight ratio of PVA to kaolin clay in the coating was determined to be 50∶50. It was assumed that the PVA/kaolin clay coating improved the smoothness of the paper considerably and decreased the pore size by filling the pores on the paper surface and forming an even film, thus enhancing the paper barrier performance. The coated paper also exhibited good repulpability.

Towards a sustainable geoliner construction in landflls by potential blending of fly ash with kaolin clay alternative:a review with an insight to Indian scenario

Electricity generated through coal-based Thermal Power Plants(TPPs)has played a pivotal role in shaping modern civiliza-tion,revolutionizing industries,and improving the quality of life for billions of people worldwide.These TPPs contribute to about 37%-40%of the global energy requirements.Energy production,in turn,has a direct impact on the economy of any country.Apart from this boon to humankind,these TPPs combusting coal as their primary fuel also have specific environmen-tal impacts,the major ones being water,air,and soil pollution due to unscientific disposal of high-quantity fly ash produced yearly.If we can put this ash to good use,it may assist us in mitigating the pollution caused by it.Although there are many conventional uses of fly ash,such as a pozzolanic material in the cement industry,more pathways need to be discovered to balance the high generation quantities with consumption.Therefore,a detailed description of its use in potential geoliner applications is presented in this article.A geoliner or a landfill liner acts as a virtually impenetrable layer to mitigate the leachate penetration into the underneath subsoil and groundwater,thus preventing contamination.There are presently some studies that support the use of only fly ash in such applications.Nevertheless,the properties of the geoliners using it are not so good to significantly mitigate environmental degradation owing to its high permeability and low densification tendency.The bentonite conventionally used has limited deposits and is mined intensively for its use as a natural sealant.Their depos-its must also be conserved,and an alternative material that may serve similar application benefits,like bentonite,must be selected.The desired aim can be fulfilled if we blend this combustion residue with other suitable materials(such as kaolinite clay)with low permeability.Thus,the article focuses on the possibilities of blending fly ash with different clays for geoliner construction to improve the individual properties of fly ash.This will contribute to developing a scope for future scientific research in deploying these blends in natural membrane materials for various industries.Different types of geoliners that are designed to contain the disposed-off waste are also explained in detail.Additionally,a glimpse of the global fly ash market is put forward to depict its importance for various industries in this technologically advancing world.This article profoundly observes an overall environmental management aspect regarding waste utilization.