Sevgi Kocaoba

Removal and recovery of chromium and chromium speciation with MINTEQA2

Chromium(III) is commonly found in large quantities in tannery wastewaters. For this reason, the recovery of the chromium content of these wastewaters is necessary for environmental protection and economic reasons. Removal and recovery of chromium were carried out by using ion exchange resins. To this purpose, two weakly acidic exchange resins Amberlite IRC 76 and Amberlite IRC 718 and a strongly acidic exchange resin Amberlite IR 120 were used. Basic chromium sulphate [Cr(4)(SO(4))(5)(OH)(2)] solutions in different concentrations and pH were used in all experiments as tanning baths. The resins were prepared in two different ionic forms as Na(+) and H(+). The effects of concentration, pH, stirring time and resin amount were investigated. The concentration range varied between 5 and 100 mg l(-1), pH range was between 1 and 8, stirring time between 5 and 60, and resin amount was between 50 and 1000 mg. Stirring speed was 2000 rpm during all these experiments. Exchange capacities, moisture contents and optimum conditions of these resins were determined in batch system. The results obtained showed that Amberlite IRC 76 and 718 weakly acidic resins had shown better performance than Amberlite IR 120 strongly acidic resin for removal and recovery of chromium(III) in Na(+) form. Optimum conditions were found as concentration 10 mg l(-1), pH 5, stirring time 20 min, and resin amount 250 mg. Furthermore, chromium(III) speciation was investigated for optimum concentration and pH with MINTEQA2 computer programme. The studied pH range was between 1 and 8 and concentration range was between 5 and 100 mg l(-1). Cr(OH)(2+) species were found to be dominant at pH 5 and 10 mg l(-1) concentration in batch studies. There was a correlation between experimental and computerised results.

Chromium(III) removal from wastewaters by a weakly acidic resin containing carboxylic groups

As a conservative technology, ion exchange allows the removal and recycling of metals from liquid effluents. A process was applied for the removal of chromium(III) from wastewaters by ion exchange. This process was based on a weakly acidic cation-exchange resin (Amberlite IRC 86) capable of removing chromium(III) from the effluent, followed by selective separation and recovery during a regeneration procedure. Because of the difficult regeneration behaviour of the metal form of the carboxylate resin, special emphasis was given to the regeneration step of the resin where most of the practical problems were found. Five different regeneration procedures were adopted: elution with 1 M NaOH; elution with 1 M H2SO4; elution with 1 M NaOH followed by 1 M H2SO4 or vice versa; elution with NaOH followed by 1 M H2SO4/Na2SO4 solution; and elution with alkaline H2O2/NaOH solutions followed by 1 M H2SO4. A non-conventional regenerant solution such as hydrogen peroxide in an alkaline medium seemed very promising. The anionic species formed (chromate) was eluted quantitatively from the cation-exchange resin and separated. The regeneration efficiency of chromium(III) was 89.5%. Influent chromium concentrations employed during the tanning process used in the leather industry were also considered. For this purpose, influent concentrations in the range 60–100 mg/l, service flow rates of 10 and 20 l/h and appropriate retention times were selected and experiments undertaken in a column system. The exhaustion step was carried out at 250 l/h with the recovery of chromium being 95.6%. The ion-exchange capacity of Amberlite IRC 86 was found to be 1.28 equiv/l. This study undertaken under laboratory conditions demonstrated that Amberlite IRC 86 resin was suitable for the removal of chromium(III) from wastewater.

A Kinetic Investigation of Chromium

A kinetic investigation was performed with an ion exchange resin for chromium. A chelating cation exchange resin (Amberlite IRC 718) was used for removal and recovery of chromium. The effect of concentration, resin amount, particle size and stirring speed on kinetics were investigated. The metal concentration range studied was between 5 to 160 mg L−1, the resin amount range was between 5 to 20 mg, the particle size range was between 0.35 to 1.8 mm and the stirring speed range was between 1000 to 3500 rpm.Kinetic studies were done using a Kressman-Kitchener stirrer reactor system and the results were compared with existing kinetic models. Two models; Nernst-Plank film diffusion control model (fdc) and solid phase diffusion control model (pdc) were identified and the dependence of the rate on parameters, such as solution concentration, particle size, resin amount, stirring speed, etc., was examined for each of them. As a result, interpretation of these data showed that the system is probably controlled both film and particle diffusion.

Behaviour of Cadmium(II) Ions on Cation-exchange Resins

Cadmium is one of the most toxic heavy metals known and is considered inessential for living organisms. This element is found at low concentrations in natural environments, but human activities have led to increased levels in all continents. In the present study, the removal of cadmium(II) ions from aqueous solutions was investigated. Experimental investigations were undertaken using the ion-exchange resins Amberlite IR 120 (strongly acidic), Amberlite IRC 718 (weakly acidic and chelating), Lewatit TP 207 (weakly acidic and chelating) and Lewatit CNP 80 (weakly acidic). For investigations of the exchange equilibria, different amounts of resin material were contacted with a fixed volume of a cadmium ion-containing solution. Because the uptake of cadmium ions was mainly dominated by the pH of the liquid phase, the pH value was varied between 0 and 3 with sample sizes of 0.5–5.0 g in each series studied. The initial and final cadmium ion concentrations were measured by ICP–AES methods. Exchange equilibria were evaluated for strongly and weakly acidic resins via the surface complex formation theory that considers the sorption of ions as a local equilibrium reaction caused by the amphoteric behaviour of the surface. Application of this theory to exchange equilibria with ordinary and chelating weak acid exchange resins capable of releasing protons led to a comprehensive description of the systems. Binary equilibria were described by a logarithmic equilibrium parameter that was a linear function of the resin phase. For the evaluation of the equilibrium parameters, the generalized separation factors were calculated from the experimental data and plotted against the respective dimensionless resin loadings. Linear relationships were obtained in most cases although systematic deviations were found for small loadings.

Removal and Recovery of Chromium from Solutions Simulating Tannery Wastewater by Strong Acid Cation Exchanger

The process in this study was conducted on removal of chromium(III) in a solution simulating a typical spent chrome tanning bath by the resin having matrix of styrene-divinylbenzene-based macroporous sulphonate, Amberjet 1200Na. The column experiments were carried out with the bed volumes of the resin as 751 mL and 1016 mL for different installation systems of the laboratory-scale pilot plant. The feeding solutions in the bed volumes of 200 and 190 were used for each installation system. The regeneration behaviour of the resin was determined by using reverse regeneration procedure with the solution of hydrogen peroxide in alkaline. The regeneration kinetics of the exhausted resin was examined with a range of the solutions having different concentration series of the alkaline hydrogen peroxide. The solutions of the basic chromium sulphate were recycled for each installation system following the regeneration cycles. The chromium ions in effluent were quantitatively eluted, and satisfactory removal of chromium(III) and recovery of chromium(VI) were achieved.

Cation Exchange Equilibria with Chromium (III) Species by Strong Acid Ion Exchangers

The exchange of hydrogen ions for trivalent chromium species with strongly acidic exchange resins has been investigated. The experiments comprised of systems with chromium chloride and basic chromium sulphate which are applied in leather tanning. Exchange equilibria at ambient temperature were investigated as a function of pH and total chromium concentration. Exchange strongly depends on the speciation in each system. As can be expected, with chromium chloride solutions a strong preference of chromium species occurs. However, a complete pattern is found for systems with basic chromium sulphate where chromium species are not fully preferred.

No-Aqueous Titrations: Potentiometric Titration of Some Primary Amines

Potentiometrie titrations of some primary amines; 1-aminobutane, 1aminopropane and 3-amino-l-phenylbutane were carried out with hydrochloric acid in toluene solvent. The same titrations were done with hydrochloric acid in methanol solvent to show the effect of amphiprotic solvent in the titrations with hydrochloric acid. For each weak base, an Sshaped Potentiometrie titration curve was obtained. As a result, toluene, which is an aprotic inert solvent, is a suitable solvent for titrating some of the weak bases potentiometrically.

Potentiometrie Titration of P-Anisidine and P-Toluidine in Non-Aqueous Media

Potentiometrie titrations of p-anisidine and p-toluidine were carried out with hydrochloric acid in toluene solvent. The same titrations were done with hydrochloric acid in methanol solvent to show the effect of amphiprotic solvent in the titrations with hydrochloric acid. For each weak base, an Sshaped Potentiometrie titration curve was obtained. As a result, toluene, which is an aprotic inert solvent, is a suitable solvent for titrating some of the weak bases potcntiometrically.

Biosorption of cadmium(II) and lead(II) from aqueous solutions using Pleurotus ostreatus immobilized on bentonite

ABSTRACT The purpose of this work was to evaluate the potential of a white rot fungi (P. ostreatus) immobilized on bentonite, in a continuous flow removal of trace heavy metals. The procedure is based on the biosorption of Cd(II) and Pb(II) ions on a column of bentonite loaded with dried, dead fungi components prior to their determination by atomic absorption spectroscopy (AAS). Cd(II) and Pb(II) were determined with a relative error of less than 5%. Various parameters such as “pH, amount of adsorbent, eluent type and volume, flow rate of the solution and matrix interference effect” on the retention of the metal ions were investigated. This procedure was applied to Cd(II) and Pb(II) determination in aqueous solutions, including tap water system. The optimum experimental parameters were determined to be pH 5, concentration of 10 mg/L, contact time of 30 min and 0.2 g of adsorbent for a quantitative adsorption of the metals. The optimum flow rate was found to be 2.5 mL/min for all metal ions. Each column can be used up to 20 successive analyses without considerable change in recoveries of metal ions. The proposed method is excellent as regards simplicity, sensitivity, selectivity, precision, accuracy and column stability.

A Potentiometric Investigation of Primary Amines in Non-aqueous Media

Titration of weak bases in non-aqueous solvents can provide valu- able information about these weak bases. Some primary amines; 1-aminobutane, 1-aminopropane, 2-aminoheptane, aminocyclohexane, 3-amino-1-phenylbutane were titrated with hydrochloric acid in toluene solvent. All the primary amines gave very well-shaped potentiometric titration curves. The same titrations were done with hydrochloric acid in methanol solvent to show the effect of amphiprotic solvent in the titrations with hydrochloric acid. As a result, toluene is a suitable solvent for titrating some of the primary amines potentiometrically with hydrochloric acid.