Structural and Textural Modifications of Palygorskite and Sepiolite Under Acid Treatment

Abstract

Abstraet--Sepiolite from Mara (Zaragoza, Spain) and palygorskite from Attapulgus (Georgia, USA) were activated by treatment at different concentrations with solutions of boiling HC1 under reflux conditions. The natural and treated solids were characterized by mineralogical, chemical and textural analyses.Acid attack resulted in a progressive dissolution of the octahedral layer of these silicates. Silica contents increased and octahedral cations (A1, Mg and Fe) decreased with the intensity of the acid attack. In both cases, fibrous free silica was obtained.The sepiolite was destroyed more rapidly than palygorskite under the conditions used because of its magnesic composition and the larger size of its structural microchannels. The maximum increase in specific surface area was obtained for sepiolite at 3 N and for palygorskite at 9 N. Cleaning and disaggregation of the particles and the increase in the number of micropores were responsible for this increase in specific surface area.

Catalysis by <i>Candida antarctica</i> B (CALB) immobilized on natural pure silica by adsorption: comparison with the free enzyme

“…Due to the relatively high cost of activated carbons, there have been attempts to utilize low cost, naturally occurring adsorbents for immobilization. In recent years, there has been increasing interest in utilizing natural clay minerals like montmorillonite (Ramos et al, 2014), bentonite (Yesiloglu 2005), and sepiolite (Myriam et al,1998) or natural polymers (Lv et al, 2008, Ittrat et al,2014, Pereira et al,2003, Ramani et al,2010 can also be used as support for the immobilization of enzyme. They are natural matrices resulting from agricultural waste, which contain cellulose, hemicellulose and lignin for this process.…”

“…Catalysis by Candida antarctica B (CALB) immobilized on natural pure silica by adsorption: comparison with the free enzyme contained in bentonite support (70 -80 %) (Yesiloglu 2005), and largely higher than is contained of montmorillonite (50-60 %) (Ramos et al, 2014), sepiolite (69.1%) and the palygorskite (70%) (Myriam et al, 1998). Biochemical properties of free and immobilized lipase pH stability and optimum pH: The effect of pH on the stability of both free and immobilized lipase was determined by measuring the residual conversion of oleic acid in the pH range of 6.0-8.0 and the results were presented in figure 1.…”

Análisis del tratamiento en medio ácido de partículas de pizarra

“…Como es bien sabido, la fórmula química del cuarzo es SiO 2 , la de la moscovita puede representarse como KAl 2 (AlSi 3 O 10 ) (OH) 2 , y la de la clorita como (Mg, Fe) 3 (Si, Al) 4 O 10 (OH) 2 (Mg, Fe) 3 (OH) 6 . La presencia de Na, Ca y otros elementos en la pizarra es debida a los feldespatos y a impurezas existentes en ella.…”

“…Estos cambios superficiales son de gran importancia para las aplicaciones posteriores de dichos minerales: decolorantes, adsorbentes, catalizadores y soportes de catalizadores, portadores de pesticidas, etc. (2)(3)(4). Por lo que respecta a la pizarra, ésta ha sido muy poco utilizada en otras aplicaciones distintas a las de techado de edificios o plaquetas para cubierta de suelos y paredes.…”

“…La intensidad del tratamiento dependerá de factores tales como la naturaleza y concentración del ácido utilizado, el tiempo de tratamiento y la temperatura. Son muchos los trabajos que han demostrado este tipo de activación (1,4,(7)(8)(9).…”