Characterization of products obtained by acid leaching of Fe-bentonite

Abstract

AB ST R ACT : This study focused on the structure and physical properties of acid-treated bentonite L45 from the Lieskovec deposit (Slovakia). New applications of near infrared and visible spectroscopies were used to follow Fe-montmorillonite dissolution and layer-charge reduction. Progressive dissolution of L45 results in the formation of a protonated amorphous silica phase. The OH overtone at 7312 cm À1 revealed the creation of SiÀOH groups in the mildly treated samples. The area of the SiÀOÀM oct band, as obtained by a peak-fitting procedure, is a sensitive indicator of the changes in the octahedral sheets. Ultraviolet-visible (UV-VIS) spectroscopy of the smectite dispersions with methylene blue (MB) is an efficient method for controlling the acid activation process of bentonites. The results reveal that acid treatment causes a substantial layer-charge reduction, probably due to prevailing dissolution of MgO 4 (OH) 2 polyhedra in the octahedral sheets. The layer-charge reduction is proportional to the structural changes and to the extent of mineral decomposition upon acid treatment.

Adsorption Behavior of Acid-Leached Clays in Bleaching of Oil

“…Removal of octahedral ions left a silica skeleton with enhanced adsorptive properties [38]- [40]. Langmuir constants given in Table 3 decreased with increasing temperature for all clays used, indicating increasing availability of adsorption sites with elevated temperatures because all sites were not energetically equal [17].…”

“…This evidence is also used to indicate that the water or hydroxyl groups in the clays play a major role since the gradient of the graphs in Figure 5 increased with increase the concentration of the acid used to leach the clay depicting that acid-activation of the clay greatly enhanced the bleaching capacity of any clay because acid-leaching removed octahedral ions like sodium, magnesium, calcium and potassium ions from the clay matrix which was established to retard bleaching [37] [40]. The heats of adsorption, ∆Ha, in kJ·mol −1 obtained from the slopes of the lines obtained in the plot of lnxe versus 1000/T are given in the Table 9.…”

Electrochemical activity of iron in acid treated bentonite and influence of added nickel

“…The dissolution of tetrahedral sheets is the stage that requires the most severe conditions. Under conditions commonly used for acid activation the changes occur even in the tetrahedral sheets [19][20][21][22]. In order to analyze the effect of the applied acid treatment on exchangeable cations, octahedral and tetrahedral cations the chemical analysis was performed.…”

“…This process is followed by the dissolution of structural cations in octahedral smectite sheets. The dissolution of tetrahedral cations and amorphization occurs under more severe conditions of acid activation [19][20][21][22]. The extent of acid activation can be controlled by several factors: the concentration of acid, the ratio between bentonite and acid solution amounts, temperature and the duration of contact time between acid and bentonite [20].…”

How Variation of Turbidity of Bleached Oils Characterizes Purity Oil and Bleaching Processes

“…Acid-leaching removed octahedral ions like sodium, magnesium, calcium and potassium ions from the clay matrix which retard bleaching (Balaras et al, 1999). Removal of octahedral ions left a silica skeleton with enhanced adsorptive properties (Boyd, 1988;Hassan, 2006;Madejova, 2007). Langmuir constants decreased with increasing temperature for all adsorbent systems used.…”