Preparation and characterization of nanoporous powders from bentonite by hydrochloric acid leaching and using as bleaching earth

Abstract

A calcium bentonite (CaB) was leached by hydrochloric acid (HCl) solutions to improve the adsorptive properties such as nanoporosity, acidity, and decoloration power. The mass ratio of HCl/CaB was changed between zero and 1.00 according the anhydrous CaB + HCl mixture. Different powders were obtained from the heating of the aqueous mixtures at 90 °C for 16 h under a reflux condenser. The raw CaB and obtained powders were investigated by different methods such as X-ray diffraction, chemical analyses, adsorption, pH-metry, and tintometry techniques. A calcium rich-smectite (CaS) are found in the CaB as major clay mineral, whereas illite (I) and metahalloysite (MH) as minor ones. The impurities are opal-A (OA), opal-CT (OCT), quartz (Q), calcite (C), orthoclase (O), and clinoptilolite (CLN). The fraction of the dissolved cations from the C, CaS, I, and CLN increases with the increasing of HCl concentration. The remaining K + and Al 3+ cations are located in the undissolved orthoclase. An amorphous silica OA (SiO 2 •nH 2 O) remained at the end of completed leaching. The gradual increase in the adsorptive properties, acidity, and bleaching power is due to the formation of new nanopores. Gradual decrease after their maxima is caused from the degradation of the layered structure for clay minerals. The maximum bleaching power tentatively intensifies with the increasing of the used powder mass.

Possibility of bleaching sunflower oil with synthetic zeolite

“…Therefore, in the industrial production of edible vegetable oils, the bleaching procedure of previously neutralized crude oil plays a major role, in which unwanted substances are removed by applying a suitable adsorbent [2], which enables the production of commercial oil of the quality prescribed by relevant national regulations. Natural and active clays are usually used as bleaching agents for edible vegetable oils [3], [4], and clay activation is usually done with inorganic acids such as H2SO4 [5], [6] and HCl [7], [8]. The goal of activation is to improve the physical and chemical properties responsible for the removal of unwanted substances from oil [9], and refers, among other things, to the increase of adsorption capacity [10], specific surface area and microporosity of clay [11], [12], [13].…”

The Influence of the Used Bleaching Earth on the Content of Natural Dyes in Hemp (Cannabis sativa L.) Oils

“…Therefore, removing chlorophyll pigments by bleaching will positively affect the sensory properties and extend the shelf life of vegetable oils. This process involves the adsorption of undesirable substances by bleaching earth [20], silica gel [21] and activated carbon [22]. Bleaching earths are mineral clays of aluminum silicates, such as bentonite, attapulgite, or sepiolite [23][24][25].…”

Reuse of Bleaching Earth: The Green Solution for Rapeseed Oil Producers

“…The main result of oil refining is an increase in their oxidative stability, thanks to which they can be, among other things, stored longer [21,22]. One of the refining stages is the bleaching process, mainly consisting of the removal of chlorophyll and carotenoid dyes with the use of various types of adsorbents, i.e., bleaching earth [23][24][25], silica gel [26], and active carbon [27]. It is crucial to properly select the bleaching parameters and optimize this process.…”