Mehmet S. Çelik

Adsorption of cobalt from aqueous solutions onto sepiolite

Adsorption of Co(II) ions from aqueous sepiolite suspensions has been systematically investigated as a function of several variables including activation conditions, solid to liquid ratio, pH and temperature. The results are analyzed to identify the mechanism of cobalt uptake by sepiolite. Both abstraction and real adsorption isotherms were constructed to isolate the precipitation of cobalt from the real adsorption. Also, for the first time a plausible correlation between the released Mg(II) ions from sepiolite matrix and those adsorbed Co(II) ions is made. A one to one ion exchange mechanism is found to describe the results. The data obtained from adsorption isotherms at different temperatures were fitted to various adsorption models to calculate thermodynamic quantities such as the free energy of adsorption, heat of adsorption and entropy of adsorption. The thermodynamic data indicate that Co(II) adsorption onto sepiolite is entropically driven and characterized by physical adsorption.

Adsorption mechanism of cationic surfactants onto acid- and heat-activated sepiolites

Systematic adsorption tests were carried out to determine the uptake of typical quaternary amines, dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide and a primary amine, dodecylamine hydrochloride by sepiolite. Bottle adsorption tests conducted with untreated, acid- and heat-activated sepiolites exhibit two distinct regions. The first stage is characterized by low rate and governed through an ion exchange process between ammonium ions and magnesium ions in the octahedral sheet. The second stage is ascribed to a combination of chain-chain interactions through Van der Waals forces and ion exchange process. Despite several-fold increases in surface areas upon activation, surprisingly no improvement in adsorption is observed. The observed differences are explained on the basis of partial collapse of the sepiolite crystal structure, the removal of zeolitic and bound waters and modification of the pore size distribution of sepiolite upon treatments.

Electrokinetic properties of clinoptilolite with mono- and multivalent electrolytes

In this study, electrokinetic properties of clinoptilolite have been determined. A series of systematic zeta potential measurements have been performed to determine the isoelectric point (iep) and potential determining ions (pdi), and the effect of mono- and multivalent salts such as NH4Cl, CaCl2, Al(NO3)3 on the zeta potential of clinoptilolite. Clinoptilolite in water exhibits a negative surface charge and maintains this character even in very acidic conditions of pH 2–3. This reveals that clinoptilolite has no iep in the pH range of 2–12. H+ and OH− ions are the pdi for clinoptilolite. Excluding the trivalent Al3+ cations, monovalent and divalent cations are not able to reverse the surface sign of clinoptilolite. This is attributed to the ion exchange ability of clinoptilolite and the strong specific adsorption of the Al3+ counterions. A schematic adsorption model which accounts for the adsorption of mono- and multivalent ions in the electrical double layer of clinoptilolite is proposed.

ADSORPTION MECHANISM OF QUATERNARY AMINES BY SEPIOLITE

A series of adsorption tests examined the uptake of typical quaternary cationic surfactants, dodecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide from water by a clay mineral, sepiolite. Adsorption tests conducted under different conditions revealed that sepiolite is highly receptive to adsorption of cationic surfactants. Adsorption of cationic surfactants on sepiolite exhibits two distinct regions. The first stage is characterized by low rate and is governed through an ion-exchange process between ammonium ions and magnesium ions in the octahedral sheet. The second stage is ascribed to a combination of chain–chain interactions through van der Waals forces and ion-exchange process. The incorporation of surfactant ion is elaborated on the basis of experimental data and thermodynamic equations.

EFFECT OF HYDROCARBON CHAIN LENGTH ON ADSORPTION OF CATIONIC SURFACTANTS ONTO CLINOPTILOLITE

The adsorption behavior of quaternary ammonium cationic surfactants with different hydrocarbon chain lengths, i.e. HDTMA (hexadecyltrimethylammonium), TDTMA (tetradecyltrimethylammonium) and DDTMA (dodecyltrimethylammonium), onto clinoptilolite has been investigated. The adsorption isotherms of these surfactants are correlated with the ζ potential curves of clinoptilolite. Accordingly, the applicability of the hemimicelle hypothesis to the adsorption of cationic surfactants at the clinoptilolite/water interface considering in the electrical double layer (EDL) of clinoptilolite is discussed. Even though the adsorption occurs in the EDL of clinoptilolite, the adsorption of HDTMA, TDTMA and DDTMA onto clinoptilolite is not conveniently described by the hemimicelle hypothesis. The absence of all expected marked increase in the ζ potential curves at the hemimicelle concentration is ascribed to the large external cation exchange capacity of clinoptilolite. The hydrocarbon chain length of surfactant molecules is found to have a significant effect on the ion exchange as well as hydrophobic interaction mechanisms. The effectiveness of both ion exchange and hydrophobic interactions increases with increasing chain length, and so the greatest surfactant adsorption onto clinoptilolite was obtained by HDTMA.

Effect of Ultrasonic Treatment on the Floatability of Coal and Galena

Abstract The effect of ultrasonic pretreatment on the floatability of coal and galena is examined. Sonication of coal treated with oxidizing and reducing agents prior to flotation is found to completely restore its hydrophobicity. Flotation of galena by xanthate under incipient collector conditions is improved by using different treatment modes. Sonication in the absence of collector followed by slime removal and conditioning with collector resulted in recoveries several times higher than those in the absence of sonication. A mechanism involving the formation of clean surfaces followed by the occurrence of microbubbles on the hydrophobic solid and the resultant enhancement in bubble-particle attachment is proposed to be responsible for improved recoveries. The results further demonstrate that ultrasonic treatment under appropriate conditions can achieve at least a 50% reduction in collector consumption in the galena/xanthate system.

FLOTATION MECHANISMS OF BORON MINERALS

Abstract The development of reagent strategies for the flotation of boron minerals requires an understanding of flotation chemistry of reagent/mineral interactions. The floatability of a typical boron mineral, colemanite, was investigated in a microflotation cell by using anionic and cationic surfactants as collectors and tannic acid as a depressant. The results obtained with zeta potential measurements together with flotation tests reveal that colemanite is floatable with both anionic and cationic surfactants at its natural pH of 9.3. While the floatability of colemanite with anionic surfactants decreases with increasing pH, that with a cationic surfactant exhibits a maximum at pH 10.2, indicating the major role of electrostatic interactions in the system.

Adsorption of ethoxylated sulfonate and nonionic homologs on coal

Abstract The adsorption of ethoxylated sulfonates and nonionics of the same ethoxylation number on a low-ash coal has been studied. The surfactant adsorption has been investigated as a function of concentration, pH, temperature, and ionic strength for three homologs. The zeta potential of the coal particles and the surface tension of the supernatants have been concurrently determined to elucidate the orientation of surfactant molecules on the coal surface as well as the mechanism of adsorption. The adsorption data are utilized to calculate thermodynamic parameters such as the free energy of adsorption and the isoteric heats of adsorption.

Effects of bivalent salts on the flotation separation of Na-feldspar from K-feldspar

Despite similarities in the physical and physico-chemical properties of Na- and K-feldspars, their flotation separation with monovalent ions exhibited a reasonable success. Further studies have been therefore initiated to ascertain whether multivalent ions, i.e., Ca and Ba can widen the window of separation of individual feldspar minerals. Upon addition of multivalent ions, ion exchange between the added ions and those in the crystal lattice and ion adsorption in the electrical double layer occurs. The ionic size of Na and Ca cations and those of K and Ba cations are almost the same indicating the ability of exchange among each couple. The compatibility of this exchange determines the extent of surface modification with the added ions. In this study, amine flotation together with zeta potential measurements has been studied as a function of bivalent salts to understand their effects on differential separation of feldspar minerals. It is found that bivalent ions exhibit complex and yet interesting features of adsorption and ion exchange patterns. The mechanism of action is elaborated on the basis of flotation and zeta potential data.

Flotation separation of Na-feldspar from K-feldspar by monovalent salts

A major proportion of feldspar ores contain both Na-feldspar (Albite) and K-feldspar (microcline or orthoclase) in the same matrix, usually in quantities of about 3-F% NazO and KsO. Despite their identical crystal structures and physicochemical properties, flotation appears to be the only plausible method of separating these minerals. In this study, amine f7otation together with zeta potential, solubility, surface tension, and adsorption measurements has been studied as a function of monovalent salts in order to achieve a window of separation. The results reveal that at a particular salt concentration of NaCl and KClflotation is maximised. A mechanism based on the adsorption of common ions, and ion exchange between the added salt of uncommon ions and those ions in the crystal matrix and the resultant surface modification is proposed to be responsible for the observed selective separation. 0 2001 Elsevier Science Ltd. All rights resewed.