Eyüp Sabah

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.

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.

Zeta Potentials of Sepiolite Suspensions in Concentrated Monovalent Electrolytes

Abstract Sepiolite is a hydrated magnesium silicate with a fibrous structure. It undergoes acid‐base interactions around the natural pH of 8.5. The zeta potential (zp) of sepiolite depends on the type, the chemical, and the mineralogical composition of sepiolite and more importantly the ionic environment of the suspensions. In this study, electrokinetic properties of sepiolite have been determined. A series of systematic zeta potential measurements have been performed to determine the isoelectric point (iep), the potential determining ions (pdi), and the effect of monovalent ions on the zeta potential of sepiolite. The electrokinetic behavior of sepiolite was examined in the presence of monovalent ions to identify if they adsorb through ion exchange or get incorporated in the diffused layer. A schematic ion adsorption/ion exchange model which illustrates the arrangement of monovalent ions in the electrical double layer of sepiolite is proposed.

Unexpected difference in phenol sorption on PTMA- and BTMA-bentonite

The comparison of phenol sorption on phenyltrimethylammonium (PTMA)- and benzyltrimethylammonium (BTMA)-bentonite shows a clear difference as far as phenol sorption isotherms are concerned. For PTMA-bentonite the sorption isotherm is of a straight-line character which results from simple partitioning of phenol between the aqueous and organic phases sorbed on the bentonite surface. For BTMA-bentonite the isotherm has a convex shape, characteristic of physicochemical sorption. For the first time a three-parametric model, including the dissociation constant of phenol pK(a), distribution constant of phenol Kd(phen) and phenolate anion Kd(phen)(-) between the aqueous phase and the bentonite phases is used for the evaluation of phenol sorption on organoclays with pH change. The model shows that the values of Kd(phen) are higher than those of Kd(phen)(-) for all investigated initial phenol concentrations. The inspection of the FTIR spectrum of BTMA-bentonite loaded with phenol in the regions 1300-1600 and 1620-1680 cm(-1) shows the features of pi-pi electron interaction between the benzene rings of phenol and the BTMA cation together with the phenol-water hydrogen bond strengthened by this interaction.

Modeling and optimization of fine coal beneficiation by hydrocyclone and multi-gravity separation to produce fine lignite clean coal

ABSTRACT We evaluated the suitability, contribution to the national economy, and environmental impact of hydrocyclone and Multi-Gravity Separation (MGS) processes using fine-sized coal taken from the Soma coal sludge pond. The lignite coal tailings were treated by a two-stage concentration scheme for the recovery of fine clean coal. Pre-enrichment experiment parameters were determined by the Taguchi experimental design method, and the results were interpreted by the Statistical Packages for the Social Sciences (SPSS) 15.0 program to evaluate the optimum parameter values. The tailings initially contained 54.82% ash and had a LCV of 2,279 kcal/kg; after hydrocyclone pre-enrichment, the concentrate was 42.60% ash and had a calorific value of 2,573 kcal/kg (55.75% coal yield). After the final enrichment process, the ash of the pre-concentrated coal was decreased to 24.21% and left a clean coal with a base calorific value of 3,226 kcal/kg (36.16% coal yield). The total sulfur of the obtained clean coal was 0.52% and the combustible sulfur rate was 0.10%. To reduce the ash content of the obtained clean coal, a decantation process was performed that decreased the ash content to 21.84% and the base calorific value was increased to 4,109 kcal/kg.

İnce Boyutlu Kömür Hazırlama Tesisi Atıklarının Geliştirilmiş Gravite Yöntemleri ile Zenginleştirilmesi

Gecmis yillarda, ince komurlerin degerlendirilmeden atilmasi daha ekonomikti. Gunumuzde ise; madencilik, atiklarin bertarafi ve stoklama maliyetlerindeki artis ince fraksiyonlardaki komurun degerlendirilmesini gerekli kilmaktadir. Bu arastirma, Garp Linyitleri Isletmesi (Tuncbilek-Kutahya) -0,1 mm komur hazirlama tesisi atiklarinin zenginlestirilemesi icin uygulanan deneysel calismalari icermektedir. Karakterizasyon calismalari sonucunda, komur atiklarinda linyit komurunden daha yuksek yogun degerlerine sahip kil mineralleri (kaolinit, mika/illit ve smektit grubu), kuvars, siderit, pirit ve dolomit bulundugu belirlenmistir. Zenginlestirme prosesi on ve nihai proseslerden ibarettir. iki asamali on zenginlestirme testlerinde, komure eslik eden kil minerallerini ayirmak icin hidrosiklon kullanilmistir. Bu amacla, hidrosiklon ve Falcon konsantratorunun yapisal ve operasyonel parametreleri (hidrosiklon capi, vortex ve apex capi, besleme giris basinci, pulp kati orani; santrifuj kuvvet, besleme hizi, pulp kati orani ve yikama suyu basinci) optimize edilmis ve bu parametrelerin ayirma performansina etkisi tartisilmistir. Optimum sartlarda elde edilen ince temiz komurun kul ve kukurt orani %35,66 ve %1,63 olup, komur kazanma verimi ise %34,60’dir.

Mechanistic insight into pyrene removal by natural sepiolites

This paper investigates the sorption characteristics and mechanisms of pyrene onto two types of natural sepiolite-brown (B-Sep) and white (W-Sep). The effects of relevant properties such as clay content, surface area, pore diameter and volume, divalent cations, and organic carbon content were investigated by single component batch adsorption systems. The results suggest that pyrene has high affinity for both sepiolite and its sorption behavior could be mainly affected by exchangeable strongly hydrated cations such as Ca2+ and H2O in the zeolite-like channels and by open channel defects (OCD) structures but no so much by the large number of Si-OH groups located on the sepiolite’s basal surfaces. Mesoporosity rather than surface area largely controls the sorption capacity and intensity of both sepiolites. This is shown by the increase in pore volume that exhibited the greatest increase in BET surface area. Particle size and morphological changes of both sepiolites following pyrene adsorption determined by FE-SEM showed that the sepiolite fibers are much longer than their widths, which are only several laths (several nanometers). This is a result of growth, mostly along the c-axis, at the expense of the diffusion of pyrene molecules through aqueous solution. As a consequence, a significant fibrous morphology is produced following the adsorption of pyrene by both sepiolites.

ADSORPTION OF PYRENE FROM AQUEOUS SOLUTIONS ONTO SEPIOLITE

Polycyclic aromatic hydrocarbons (PAHs) are a large class of organic compounds which are commonly mentioned and have been shown to be highly carcinogenic and to persist in the environment for many years. An inexpensive remediation method has yet to be found, so the current study was undertaken to test the use of sepiolite, a fibrous clay mineral, as a potentially inexpensive and effective solid-phase adsorbent for sequestering PAHs. Pyrene was chosen as a model PAH due to the specific volatility, miscibility, and relatively soluble properties of the compound. A sepiolite of Turkish origin was then investigated to explore its potential to adsorb hydrophobic organic compounds from aqueous solution. The microstructure and morphology of the sepiolite were characterized using elemental analysis, X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), and specific surface area from N2 adsorption isotherms. The pyrene adsorption isotherms were closely fitted to the Langmuir model and the coefficients of determination (RP2) were higher than 0.999. The results indicated that the high affinity of pyrene for sepiolite surfaces was dominated by the structural channels and the large number of Si-OH groups located on the basal surfaces. The intracrystalline interactions of pyrene with the sepiolite were, however, more favorable than pyrene interactions with sepiolite surface Si-OH groups, which can react directly with pyrene to form true covalent bonds (chemical interactions). Finally, the FE-SEM images initially revealed that, after sepiolite was loaded with adsorbed pyrene, a fairly straight and rigid arrangement of fibers occurred due to the aggregation of laths to form rods and the increased amounts of adsorbed pyrene.