Feasibility of compacted attapulgite/diatomite amended clayey soils as gas barrier materials

Compacted clay liners are extensively used as barriers to control the upward diffusion of vapors of volatile or semi-volatile organic contaminants released from unsaturated contaminated soils at industrycontaminated sites.This study aimed to investigate the gas diffusion barrier performance of compacted clayey soils amended with three agents including attapulgite and diatomite individually,and attapulgite/diatomite mixture.The properties including water retention,volumetric shrinkage,gas diffusion,and unconfined compressive strength were evaluated through a series of laboratory tests of amended compacted clayey soils.The results demonstrate that the decrease in volume proportions of interaggregate pores leads to an increase in unconfined compressive strength(qu).Both hydrophilic groups and microstructures of attapulgite and diatomite result in an increase in water retention percent(Wt)of compacted clayey soil specimens after amendment regardless of the type of agent or initial water content(w0).Furthermore,the ratio of the gas diffusion coefficient(De)to the gas diffusion coefficient in the air(Da)was significantly reduced owing to a decrease in volume proportions of inter-aggregate pores,hydrophilic group,and microstructures of attapulgite and diatomite.Scanning electron microscope analyses revealed that rod-shaped attapulgite filled the inter-aggregate pores formed by clay particles,whereas the disc-shaped diatomite particles,characterized by micropores,failed to obstruct the interaggregate pores due to their larger particle size.Mercury intrusion porosimetry(MIP)analyses showed a reduction in pore volume in the inter-aggregate pores,leading to a reduction in the total pore volume for both the attapulgite and attapulgite/diatomite mixture amended clays,which is in accordance with the scanning electron microscope(SEM)results.The findings are pertinent to the practical application of compacted clay liners as gas barriers against the upward migration of volatile or semi-volatile organic contaminants at contaminated sites.

Application of Modified Attapulgite Clay as the Adsorbent in Gasoline Desulfurization

Attapulgite clay is a kind of special silicate mineral with high adsorption capacity thanks to its loose structure and porous surface. In this paper, the attapulgite clay was treated effectively with acid under microwave thermal activation and ultrasonic vibration, respectively, and characterized by XRD, N2 adsorption, FT-IR and SEM. The desulfurization performance of the modified attapulgite clay was then evaluated by using simulated gasoline as the feed. The test results showed that the thiophene removal rate increased with an increasing dosage of hydrochloric acid during microwave modification of attapulgite clay. When the concentration of hydrochloric acid reached 15%, the increase of desulfurization rate became slower, and the desulfurization rate was about 69%.

Suspension Polymerization of Methyl Methacrylate Stabilized Solely by Palygorskite Nano Fibers

A kind of fibrous clay, palygorskite （PAL）, was used as the sole stabilizer in suspension polymerization without the using of any other stabilizer usually used, especially polymeric stabilizers. In order to improve the compatibility with the organic monomer, PAL nano fibers were organically modified with silane coupling agent methacryloxypropyltrimethoxysilane （MPS）. Transmission electron microscopy （TEM） and Fourier-transform infrared （FTIR） spectroscopy results show that the hydrolyzed MPS was attached onto PAL surface through Si--O--Si bonds formation without morphology change of PAL. At a loading amount of PAL to monomer as low as 0.36 wt%, effective stabilization could be achieved. After suspension polymerization, spherical poly（methyl methacrylate） （PMMA） particles were obtained. Scanning electron microscopy （SEM） analysis on both the outer surface and the inner cracked surface of the spherical PMMA particles indicates that the PAL particles reside on the surface of the PMMA spheres. The densely stacked PAL together with attached silane coupling agent stabilized the droplets throughout the suspension polymerization.