Kemijska modifikacija prirodnog zeolita klinoptilolita - analiza ravnoteže i kinetike vezivanja kadmija i cinka iz vodenih otopina

Provedena je kemijska modifikacija prirodnog zeolita (PZ) porijeklom iz Vranjske Banje s vodenom otopinom Fe(NO3)3 u acetatnom puferu pri pH=3,6 te s otopinom NaOH i NaNO3. Dobiveni Fe(III)-modificirani zeolit (FeZ) pokazao je 3-4 puta veći kapacitet vezivanja cinka i kadmija u odnosu na prirodni. Modifikacijom nije došlo do promjena u strukturi i mineraloškom sastavu, a povećao se volumen pora i količina natrijevih iona kao rezultat ionske izmjene i neutralizacije negativnog naboja nastalog tijekom modifikacije. Upravo povećana količina natrijevih iona povećava kapacitet FeZ prema ionima cinka i kadmija. Ispitan je utjecaj pH i koncentracije otopine metalnih iona, veličine čestica i mase zeolita izražene preko S/L omjera (engl. soli/ liquid), te vremena kontakta zeolit-otopina na vezivanje cinka i kadmija na PZ i FeZ. Ravnotežni rezultati za različite koncentracije otopina cinka i kadmija i dvije veličine čestica PZ i FeZ su testirani prema izotermnim modelima: Langmuir, Freundlich, Temkin, Dubinin-Radeuskevich, Sips, Toth i Hill. Dimenzijskom analizom dobile su se vrijednosti ravnotežnih parametara koji su neovisni o S/L omjeru i početnim koncentracijama. Kinetički rezultati su testirani prema reakcijskim (Lagergren-ov model pseudo prvog reda i Ho-ov model pseudo drugog reda) i difuzijskim kinetičkim modelima (Dvostruko-eksponencijalni, Weber-Morris, Bangham, Vermeulenova aproksimacija i Model difuzije kroz laminarni film). Ustanovljeno je da je difuzija kroz česticu najsporiji stupanj koji odreñuje brzinu procesa. Iz izračunatih parametara modela dobivene su modelne krivulje ovisnosti količine vezanog metalnog iona po gramu zeolita o vremenu. Dvostruko-eksponencijalni model i model prema Vermeulen-ovoj aproksimaciji pokazali su slaganje u cijelom ispitivanom vremenskom intervalu te su odabrani za predviñanje količine vezanja cinka i kadmija za proizvoljno odabranu početnu koncentraciju. Ispitivanjem desorpcije cinka i kadmija iz zasićenih uzoraka modificiranih zeolita u ultračistoj vodi različitih početnih pH, utvrñeno je da ne dolazi do desorpcije cinka i kadmija, dok je desorpcija značajna u otopinama NaCl, NaNO3 i KCl. Tijekom četiri uzastopna ciklusa zasićivanja i regeneracije iste mase FeZ nije došlo do smanjenja kapaciteta što ukazuje na izvrsna sorpcijsko-regeneracijska svojstva FeZ.Chemical modification of natural zeolite (NZ) originated from the Vranjska Banja deposit has been performed with the aqueous solution of Fe(NO3)3 at pH=3.6 and with NaOH and NaNO3 solutions. Fe(III)-modified zeolite (FeZ) has shown 3-4 times higher capacity towards cadmium and zinc compare to the natural zeolite. The modification did not cause changes in the structure and mineralogical composition, but it increased the pore volume and the amount of sodium as a result of ion exchange and neutralization of the negative charge created during the modification. The increased sodium content is responsible for the higher removal capacity of FeZ toward zinc and cadmium. The effect of pH and concentration of the metal ions solution, the particle size and the mass of zeolite expressed by S/L ratio (solid/liquid), and the contact time of zeolite-solution, on zinc and cadmium removal on NZ and FeZ have been investigated. Equilibrium results for different concentrations of Zn and Cd and two particle sizes of NZ and FeZ have been tested according to the isothermal models: Langmuir, Freundlich, Temkin, Sips, Toth, DubininRadeuskevich and Hill. The dimensional analysis has been applied and equilibrium parameters which are independent of S/L ratio and the initial concentrations have been obtained. Kinetic results were tested according to the reaction kinetic model (Lagergren's pseudo-first-order and Ho's pseudo-second-order) and diffusion kinetic models (Doubleexponential, Weber-Morris, Bangham, Vermeulen's approximation and diffusion through the laminar film). It has been found that the diffusion through the particle is the rate limiting step of process. The model curves for metal ions uptake per gram of zeolite vs. time were obtained from the calculated parameters of the models. It has been found that the Double-exponential model and Vermeulen's approximation fit throughout the whole examinated time interval. Hence, these models have been selected for predicting the quantity of zinc and cadmium uptake at chosen time and at chosen initial concentration. The investigation of desorption of zinc and cadmium from saturated modified zeolites in ultrapure water of different initial pH has shown that saturated zeolites do not release zinc and cadmium, while they are released in NaCl, KCl and NaNO3 solutions. During four consecutive cycles of saturation and regeneration of the same FeZ mass the capacity remained unchanged, indicating excellent sorption-regeneration properties of FeZ

Evaluation of low-cost sorbents as potential materials for in situ remediation of water contaminated with heavy metals

The aim of this paper was to examine the possibilities of using various low-cost sorbents as material for permeable reactive barrier for efficient removing of lead, cadmium, copper and zinc from contaminated water. Natural zeolite (NZ), iron-modified zeolite (IMZ), apatite, concentrated apatite, kaolin and raw bentonite were examined. The batch test evaluation was used to investigate capturing of heavy metals from contaminated water onto sorbents, as well as retention strength of saturated sorbent. The change of pH values during saturation and leaching of heavy metals was performed in a slightly acidic to neutral area, confirming buffering abilities and environmental acceptability of all investigated sorbents as a material in PRB for protection of groundwater as the most valuable natural resources. The highest saturation ability towards all examined heavy metals was detected with raw bentonite and IMZ. Leaching of heavy metals at pH=2.94-2.98 was confirmed in all saturated sorbents, while at pH=6.07-6.46 it was not detected, except of Pb and Cd in raw bentonite. From the obtaned results, the recommendation for selection of sorbent for treatment of water contaminated with lead, cadmium, cooper and zinc is given

Ružička days : International conference 16th Ružička Days “Today Science – Tomorrow Industry” : Proceedings

Proceedings contains articles presented at Conference divided into sections: open lecture (1), chemical analysis and synthesis (3), chemical and biochemical engineering (8), food technology and biotechnology (8), medical chemistry and pharmacy (3), environmental protection (11) and meeting of young chemists (2)

Preparation and characterization of the sulfur-impregnated natural zeolite clinoptilolite for Hg(II) removal fromaqueous solutions

Sulfur-impregnated zeolite has been obtained from the natural zeolite clinoptilolite by chemical modification with Na2S at 150 °C. The purpose of zeolite impregnation was to enhance the sorption of Hg(II) from aqueous solutions. Chemical analysis, acid and basic properties determined by Bohem’s method, chemical behavior at different pHo values, zeta potential, cation-exchange capacity (CEC), specific surface area, X-ray powder diffraction (XRPD), scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), as well as thermogravimetry with derivative thermogravimetry (TG-DTG) were used for detailed comparative mineralogical and physico-chemical characterization of natural and sulfur-impregnated zeolites

Assessment of natural zeolite clinoptilolite for remediation of mercury-contaminated environment

The soil at ancient roasting sites in the surroundings of the Idrija mine (Slovenia) is highly contaminated with mercury. To assess the impact of mercury on groundwater by infiltration and find an eco-friendly remediation method, the leaching of mercury from the soil containing 1347 mg Hg/kg, followed by sorption of the total leached mercury on cost-effective natural zeolite (NZ) clinoptilolite, was performed. The leaching of soil in ultrapure water of pHo = 3.00–11.46 after 24 h resulted in the total leached mercury concentration in the range 0.33–17.43 µg/L. Much higher concentrations (136.9–488.0 µg/L) were determined after the first few hours of leaching and were high above the maximum permissible level in water for human consumption. The NZ showed very good sorption of the total leached mercury, with a maximum removal efficiency of 94.2%. The leaching of mercury in presence of the NZ resulted in a significant decrease of the total leached mercury (1.9–20.3 µg/L compared to 12.8–42.2 µg/L), with removal efficiencies up to 90.5%, indicating immobilization of mercury species. The NZ has a great potential for economically viable remediation of mercury-contaminated environment. However, efforts should be made in the further study of mercury leachability to reduce the mercury concentration in water to acceptable levels

Effect of the solid/liquid ratio on zinc and cadmium uptake on natural and iron-modified zeolite - Batch scale design

235-245Zinc and cadmium uptake on natural (NZ) and iron-modified zeolite (IMZ) has been investigated through the two sets of experiments, first one with varying S/L ratios at a constant initial metal concentration and second one with different initial metal concentrations at a single S/L ratio. Results confirm the importance of choosing an optimum S/L ratio in achievement of the maximum removal efficiency with the lowest zeolite mass. Two different methods for the design of batch reactor have been applied to overcome the effect of the S/L ratio. The first approach applied the operating line method with the Dubinin-Radushkevich isotherm, and the second one applied the Rayleigh's method of dimensional analysis. The excellent agreement between predicted and experimentally obtained results for the amount of metal removed per gram of zeolite as well as error functions confirm the applicability of both methods in the batch scale design independently of the S/L ratio

Modeling, Simulation, Optimization, and Experimental Verification of Mercury Removal onto Natural and Sulfur-Impregnated Zeolite Clinoptilolite—Assessment of Feasibility for Remediation of Mercury-Contaminated Soil

In this paper, a series of equilibrium and kinetic experiments of Hg(II) removal in a single-stage batch reactor on natural (NZ) and sulfur-impregnated zeolite (SZ) were performed. Batch sorption of Hg(II) on zeolites was studied using different isothermal and kinetic models. It was found to be best described by the Brouers-Sotolongo isotherm and the Vermeulen’s approximation, which were applied in optimizing the mass and contact time in two-stage cross-current and counter-current flow batch reactors based on the desired criterion of 99.9% removal efficiency. Mathematical models for minimizing zeolite mass and contact time were developed and experimentally verified. The optimum minimum masses of NZ and SZ were calculated for all systems, and a significant saving in SZ consumption was found when the counter-current design was applied. The toxicity characteristic leaching procedure (TCLP) was applied to mercury contaminated soil from the Idrija mine region in Slovenia to evaluate potential soil toxicity. The results showed that the soil is extremely contaminated and represents hazardous waste. The addition of zeolites significantly reduced the concentration of leached Hg, with the most satisfactory results obtained with SZ. It was found that at the lowest dose of 0.25 g of SZ, the leached Hg concentration was reduced below the maximum concentration criterion of 0.2 mg/L according to the TCLP test. This study revealed that SZ could be a potential sorbent for in situ remediation of mercury contaminated soil