Vassilis J. Inglezakis

Equilibrium and kinetic ion exchange studies of Pb2+, Cr3+, Fe3+ and Cu2+ on natural clinoptilolite

In the present study ion exchange of Pb2+, Cu2+, Fe3+ and Cr3+ on natural clinoptilolite is examined at 27 +/- 1 degree C and initial concentration of 10 meq/dm3. Equilibrium is favorable for Pb2+, unfavorable for Cu2+ and sigmoid for Cr3+ and Fe3+. Selectivity series deduced from equilibrium isotherms is Pb2+ > Cr3+ > Fe3+ > Cu2+, while when maximum exchange levels (MELs) are considered, selectivity series is Pb2+ > Cr3+ approximately = Cu2+ > or = Fe3+. Cu2+ manifests the higher value of diffusion coefficient in the clinoptilolite particles among the metals studied, equal to 1.40 x 10(-9) cm2/s. According to the fixed bed experiments the upflow rate (5-15 Bed Volumes (BV)) is influencing the breakthrough point for all metals studied. The breakthrough point varies between 12.3 BV for Pb2+ and 1.18 for Cu2+. Flow rate is also influencing the operating capacity, giving values between 0.433 meq/g(clinoptilolite) for Pb2+ and 0.053 for Fe3+. Breakthrough point values confirm the selectivity order deduced from the equilibrium isotherms, while operating capacity values confirm the selectivity order deduced from MEL experiments.

Ion exchange of Pb2+, Cu2+, Fe3+, and Cr3+ on natural clinoptilolite: selectivity determination and influence of acidity on metal uptake

In the present study ion exchange of Pb(2+), Cu(2+), Fe(3+), and Cr(3+) on natural Greek clinoptilolite was examined in terms of selectivity toward the above heavy metals in single- and multicomponent solutions in batch systems. Also examined are the influence of clinoptilolite on solution acidity and the effect of acidity on the ion exchange process. Clinoptilolite increases solution acidity due to the exchange of H(+) cations with the cations initially present in its structure. H(+) cations should be considered as competitive ones in ion exchange processes, and consequently ion exchange of metals is favored at high acidity values. Cu(2+) and Cr(3+) are the most sensitive cations with respect to acidity. Selectivity determination demonstrates that the selectivity at total concentration 0.01 N and acidity 2 in both single- and multicomponent solutions is following the order Pb(2+)>Fe(3+)>Cr(3+) > or =Cu(2+). This order is set since the first days of equilibration. However, Cu(2+) shows remarkable changes in selectivity and generally its uptake and selectivity are increasing with time. On the other hand selectivity in single metal solutions where acidity is not adjusted is following the order Pb(2+)>Cr(3+)>Fe(3+) congruent with Cu(2+).

4 – Adsorption and Ion Exchange

Publisher Summary This chapter deals with the phenomena of adsorption and ion exchange, and highlights their role in environmental protection. Activated carbon, silica gel, and alumina are the most popular adsorbent materials in industry due to the fact that they provide large surface areas per unit weight. Activated carbon is produced from coconut shell, wood, and bone, whereas silica gel is made of hydrated silicon dioxide. Alumina can be either mined or produced by precipitated aluminum oxide and hydroxide. There are a number of cases where carbon adsorption is preferably used in water treatment—if compounds are not compliant for biodegradation, if the molecule contains branched chairs, has a large molecular weight, and low polarity, and generally, in the case of removing organic and inorganic species, for concentrations lower than 5000 and 1000 mg/L, respectively. Besides the applications of water treatment, activated carbon is called into action for the removal of volatile organic compounds, such as solvents, toxic gases, and odors from gaseous waste streams. Ion exchange shares many characteristics with adsorption, such as mass transfer from the fluid to the solid phase; there are, however, some significant differences. In ion exchange, the ions removed from the liquid phase are replaced by ions from the solid phase. So, there actually occurs an exchange of ions and not only a removal in the latter process. This principle is the basis of use of ion exchange in removing the effects of pollution in air and water.

Modeling of ion exchange of Pb2+ in fixed beds of clinoptilolite

Abstract Ion exchange of Pb 2+ on natural clinoptilolite in fixed bed and batch operations has been studied and simple models on experimental data have been applied. The operations are conducted at ambient temperature, an initial concentration of 0.01 N and at pH 4. Paterson’s model is used to describe batch kinetics, the Langmuir isotherm is used to correlate equilibrium data and a solid diffusion controlled process is used to describe the fixed bed operation. The evaluated operating capacity is in the range of 0.21–1 meq/g and the diffusion coefficient is in the range of (0.07–5.4) × 10 −12 m 2 /s. The experimental results obtained put the basic theory under question. According to these experiments, the capacity and diffusion coefficient in fixed bed systems are flow dependent and different from those measured in the batch-reactor systems. This could be explained if the type of experimental setup influenced both the equilibrium isotherm and the system behavior.

Pretreatment of natural clinoptilolite in a laboratory-scale ion exchange packed bed

The impact of the operational and chemical conditions of pretreatment upon the effective capacity of clinoptilolite has been investigated. Pretreatment tests have been performed in an ion exchange packed bed. The parameters examined for the pretreatment solution were the volumetric flow rate, the concentration, the total volume and the pH; and for washing after pretreatment the volume of washing water used. An optimal flow rate and a minimum concentration were determined, for a pretreatment that leads to a high effective capacity of the material, while pH adjustment did not result in a higher effective capacity and one washing (10 bed volumes) after pretreatment was found to be sufficient. Furthermore, the water quality (use of tap water) as well as the surface dust of the original material (about 5% w/w) did not alter its effective capacity.

Heat of adsorption, adsorption energy and activation energy in adsorption and ion exchange systems

Abstract The heat of adsorption, the adsorption energy and the activation energy are of the most important and frequently calculated parameters in adsorption and ion exchange systems. However, in many occasions these parameters are not clearly defined, appropriate calculated or analyzed in the related literature. A characteristic example is the use of different limits used in order to identify a process as physisorption, chemisorption or ion exchange. The present paper aims at clarifying the nature of these parameters and their interrelationship in theoretical basis and to present the paradigm of ion exchange systems involving zeolites and cations as a case study. All basic theoretical issues are presented, analyzed and discussed with the support of a large number of experimental data in order to draw secure conclusions on several critical issues. In total 46 activation energy, 32 adsorption energy and 34 heat of adsorption experimental values are collected and discussed.

Handbook of Natural Zeolites

Description: Handbook of Natural Zeolites provides a comprehensive and updated summary of all important aspects of natural zeolites science and technology. The e-book contains four sections covering the relevant scientific background, established technologies, recent discoveries and future perspectives. All 28 chapters in this handbook are presented by highly respected scientists and leaders in natural zeolites science and include extensive references. The text in this e-book is supported by excellent figures and tables. As a result, novices and established scientists alike will find this comprehensive volume a great resource for years to come.

Effects of pretreatment on physical and ion exchange properties of natural clinoptilolite.

Four pretreatment procedures have been applied to natural clinoptilolite to establish the influence of the pretreatment process on the properties of the material under investigation. Modification of material properties is imposed for its use in wastewater treatment via ion exchange processes. Batch pretreatment procedures as well as continuous flow column have been studied by using sodium chloride, sodium hydroxide and nitric acid solutions in deionized water. Measurements of the effective capacity, the diffusion coefficient in the solid state and examination of the crystal structure have been employed to assess the effect of each specific pretreatment on the material under test. The effective capacity is improved in all cases, by a factor of 2.4 to 3.6, while the diffusion coefficient values depend strongly on the type of pretreatment used and fall in the range of 0.03−1.37×10−8 cm2s−2 at 20°C. The crystal structure remains unaltered as evidenced by XRD measurements.

Liquid holdup and flow dispersion in zeolite packed beds

Abstract A simple tracing method, based on residence time distribution measurements, is presented for the evaluation of the liquid holdup and dispersion in zeolite packed beds. Two tracers and two different materials, one porous (zeolite clinoptilolite) and one non-porous (SiC), were used in experiments on seven packed beds of different dimensions, operating under downflow or upflow condition, in the range of superficial velocities from 0.04 to 0.61×10 −2 m / s . The corresponding superficial Reynolds number is between 0.6 and 8.50. Drainage and tracing methods are experimentally compared. The tracing techniques tested are reliable and applicable for the determination of liquid holdup and dispersion in clinoptilolite beds. Liquid holdup, as % of void volume of the bed, is 90±10% for upflow condition, independent of the superficial velocity. For downflow condition it reaches 80% for superficial velocities greater than 0.4×10 −2 m / s . Peclet numbers were determined, giving different trends for upflow and downflow conditions. For superficial velocity near 0.4×10 −2 m / s (Reynolds number near 4) and greater, Peclet numbers are identical and in the vicinity of 0.12. A discussion is conducted in order to clarify this observation. Approximate correlations are proposed for liquid holdup and Peclet number in zeolite packed beds.

Household hazardous waste management: A review

This paper deals with the waste stream of household hazardous waste (HHW) presenting existing management systems, legislation overview and other relevant quantitative and qualitative information. European Union legislation and international management schemes are summarized and presented in a concise manner by the use of diagrams in order to provide crucial information on HHW. Furthermore, sources and types, numerical figures about generation, collection and relevant management costs are within the scope of the present paper. The review shows that the term used to refer to hazardous waste generated in households is not clearly defined in legislation, while there is absence of specific acts regulating the management of HHW. The lack of obligation to segregate HHW from the household waste and the different terminology used makes it difficult to determine the quantities and composition of this waste stream, while its generation amount is relatively small and, therefore, is commonly overlooked in waste statistics. The paper aims to cover the gap in the related literature on a subject that is included within the crucial waste management challenges at world level, considering that HHW can also have impact on other waste streams by altering the redox conditions or causing direct reactions with other non hazardous waste substances.