Kadmiyum iyonunun sulu çözeltiden pmma ve pman reçineleri üzerinde adsorpsiyon ile zenginleştirilmesi

Abstract

Çalışmada; kadmiyum iyonunun sulu fazdan PMMA ve PMAN reçineleri üzerinde tutulma oranları incelenmiş, metal iyonu konsantrasyonu atomik absorpsiyon spektrofotometresi ve kadmiyum iyon selektif elektrotla tayin edilmiştir. Bu çalışmanın esas amacı, seçilen polimerlerin Cd(II) iyonu için uygun bir adsorban olup olmadığının incelenmesi ve PMMA' daki ester grubu ile PMAN' daki nitril grubunun iyona karşı seçimlilik açısından bir farklılık oluşturup oluşturmadığının araştırılmasıdır. Bu amaçla PMMA ve PMAN polimerlerinin 1/4 ve 4/1 oranında kopolimerleri ile de çalışılmıştır. Tezin ikinci amacı ise; zenginleştirme çalışmalarında kadmiyum iyonunun konsantrasyonu tayininde, düşük konsan - trasyonlu çözeltilere iyon seçimli elektrodun kullanılabi lirliğinin incelenmesidir. Çalkalama (Batch) ve kolon yöntemlerinin kullanıldığı deneylerde, Cd(II) iyonunun adsorpsiyonunda pH' in etkisi araştırılmıştır.

In this work, cadmium is preconcent rated from aqueous phase by using poly (methyl methacrylate) and poly(meth- acrylonitrile) as adsorbants and determinated by both atomic absorption spectrophotometry and cadmium ion selective electrode. Preconcentration techniques are often required in in organic analysis, especially in trace analysis to separate elements to be determined from the interfering constituents of the sample and to improve the sensitivity of the method. Accurate analysis of various samples, especially at trace levels, is one of the most difficult and complicated analytical tasks. To obtain reliable data, the best way is to separate and preconcentrate the analytes of interest from the matrix constituents and to determine them in the isolated state. This also results in greater sensivity. After concentration; the elements can be determined by sensitive Instrumental methods such as atomic absorption spectrometry, polarography and activation analysis. An ideal method for the preconcentration of trace metals should have the following characteristies : 1. It should simultaneously allow the isolation of the analyte from the matrix and yield an appropriate en richment factor, 2. It should be a simple process, 3. It should require only few reagents in order to minimize contamination, hence producing a low sample blank and correspondingly lower dedection limit, ix 4. It should produce final solution that is readily matrix matched with a solution of an analytical calibration method. As a rule, methods for separating substances utilize differences between the distribution coefficients of the individual constituents of a mixture between two phases. A schematic diagram of separation methods with indication of the phases into which the material is distributed is presented in the table below. Trace analysis deals with the determination of trace constituents in a sample material. Three modifications of the separation methods are possible. 1. The major costituent is isolated from the sample, whereas the traces remain in solution (a macro -micro separation). 2. Trace constituents are isolated from a solid or dissolved sample, major constituents being retained in solution (a micro-micro separation). 3. Trace constituents are separated from one another after isolation (a micro-micro separation). Among the numerous preconcentration techniques used in trace element determination solid-liquid separation after adsorption of metal ions on suitable adsorbants, such as activated carbon, polimeric materials, are. simple and economic al and can be applied to many elements. Adsorption from solution is a more complicated process than adsorption of gases, first of all because in addition to the force field of the solid phase, it is necessary to take into account intermolecular interaction in the liquid phase, ions in a solution are carries of an electric charge hence, the adsorption of ions is attended by the redistribu tion of the charges and the arising of an electric field in the region of the surface layer. In practice, the ex change of ions proceeds on any solid surface in an electro lyte solution because all solids are heteropolar to a certain extent. In this work, poly (methyl methacrylate) and poly(meth- acrylonitrile) resins were used as sorbent. The structure of polymeric reagents are given below. O 3 CHö-CH L i c=o I OCH PMMA CH. ?CHrCH 2 i 3 -n 3 ON PMAN n Cadmium is an important cation in connection with the public health. The poisonous nature of cadmium is analog ous to that of mercury and arsenic. In industry/ cadmium poisoning is frequently caused when cadmium metal or cadmium alloys are heated. Among the toxic manifestations of cadmium poisoning are dermatitis, in severe cases, chest and abdominal pains are experienced. The physiological action of cadmium ions is similar to that of zinc or mercury in that the central nervous system is affected. Therefore the separation of cadmium by chromatographic methods is very important. xx Both batch and column methods were used for the separation of cadmium ion from an aqueous cadmium perchlor- ate solution. In the batch method, the effect of pH on the retention of ion were investigated. The cadmium (II) ion was collected from aqueous solutions starting from pH 3. In both homopolymers and co polymers, an increase of retentions at pH 5 then a decrease again were observed. After around pH 6, they slightly in creased. The retention of ion from aqueous phase on the polymers not exceed 70%. On the other hand, it is clearly seen that there was a maximum retention at about pH 9 in order that solubility- product constant of cadmium was passed over. In batch method, 0.2 g polymers and copolymers were added into 50 ml of 5 ppm Cd(II) solutions. All of them were mixed about 1 hour with a magnetic stirrer at 350 min"1. Ater filtrating, concentration of cadmium ion was determined by FAAS. Then f iltreted homopolymers and copolymers were washed with 2 N HC1 to take Cd ion into the solution. The metal concentration was determined by FAAS. In addition, 5 ppm and 2 ppm of cadmium ion solutions containing 2% NaCl were prepared in order to determine whether sodium ion influenced the retention of trace metal. It was found that the retentions of element by poly (methyl methacrylate) and poly (methacrylonitrile) resins were fairly low. From these results, it can be concluded that sodium ion is retained on the homopolymers and because of the higher concentration of sodium ion, the trace metal can not be retained. On the other hand, the suitability of cadmium ion selective electrode for determination of cadmium ion in the same solutions was checked. With this purpose, KN03 was added into the solutions to adjust the ionic strength. Although the electrode can be used over a wide pH range,- at high solution pH s, hydrogen ion interferes with measurements of low levels of cadmium ion. For that reason, the solutions of Cd(II) ion containing hydrochloric acid at high concentration could not be determined. x±± It was observed that ionic strength of solution, stirring rate and temperature should be controled for pre cision of the results. Since electrode potentials are affect ed by changes in temperature, samples and standardizing solutions should be. the same temperature. Because the slope of cadmium electrode varies with temperature, as indicated by the factor 2.3 RT/2 F in the Nernst equation which was given below.