The Differences in Thermal Breakdown of H2PtC16 and cisPt( NH3)2C12 in Carbon Furnace Atomic Absorption.

A study using a combination of thermogravimetric and x-ray diffraction analyses has shown that a solution of hexachloroplatinic acid (Hj'tCI(), usually used as a standard in atomic absorption spectrophotometric (AAS) measurements, was broken down to yield volatile PtCt before being converted to metallic platinum. On the other hand, a solution of cis-diaminodichloroplatinum(II) (cis-Pt(NH)zClz ; cis-DDP) was converted to metallic platinum in a single step. The differences in their thermal decomposition mechanisms could be one of the leasons as to why carbon furnace atomic absorption spectrophotometric (CFAAS) signal from Hj'tCI~ was found to be lower than that of cis-DDP in aqueous solution. INTRODUCTION Studies by earlier workers have shown differences in absorbance signals of platinum from different platinum complexes when analyses by flame AAS technique. For example, the platinum absorbance of ( H4)2PtC14 (50 ppm) is about twofold greater than that of ~PtCI6 (Macquet and Theophanides 1974) and the cis-DDP signal is about 12% higher than that of H2PtCI6 (Macquet et al. 1974). These differences are said to be due to the differences in thermal stability of the complexes. The ability of the more stable complex to survive as volatile species in the flame is greater than the less stable complexes; a volatile species is more easily decomposed to free atoms hence a higher AAS signal is obtained. (Macquet and Theophanides 197

Fractionation of particulate and vapor phase fluoride in urban atmosphere

The distribution of fluoride between particulate and gaseous phases in the urban atmosphere of an industrialized city has been investigated. A new method was developed for collection of gaseous and particulate phase of fluoride. A comparison was made between the results obtained from the proposed method with those obtained from the traditional method using mixed cellulose ester (MCE) and showed an excellent agreement. The proposed method was applied for fractionation of fluoride in urban atmosphere. The seasonal variation in concentrations of gaseous and particulate fluoride in the atmosphere of the city was also investigated and showed higher concentrations of fluoride fractions in autumn and winter seasons

Separation of Gold from Nickel, Cobalt and Zinc by a Poly(hydroxamic acid) Ion-exchange Resin

Behaviour of poly(hydroxamic acid) resin prepared from poly(ethylacrylate) towards gold, silver, copper, iron, nickel, cobalt, and zinc in dilute acid solutions was evaluated. Batch method study shows that although this resin shows high affinity towards the gold ion, it can also be used for the extraction of other metal ions. Sorptions of these metal ions by the resin column are complete and their desorptions from the column can be carried out quantitatively by suitable eluants. Further investigations show that gold can be completely separated from nickel, cobalt and zinc in addition to its separations from silver, iron and copper

Preparation of basic yttrium carbonate for phosphate removal

Removal of phosphate ions from aqueous solutions has been studied with basic yttrium carbonate (BYC) of different compositions prepared by homogeneous precipitation with yttrium chloride and urea. Higher carbonate content was obtained with higher concentration of urea. Removal of phosphate was significant at pH less than 12 and dependent on the composition of BYC. The possible mechanism for removal is ion exchange with carbonate or hydroxide groups between pH 7 and 12 and through complex formation of phosphate with yttrium ions and ion exchange between pH 2 and 6. The phosphate adsorption capacity of BYC prepared with a higher concentration of urea was higher than that of BYC prepared with a lower urea concentration. The removal of phosphate followed a Langmuir model. The BYC of higher carbonate content gave higher percentage removal in the pH range of 6 to 11. The high phosphate adsorption capacity of the compound can be attributed to its carbonate group content and surface area. The phosphate adsorption was not affected by F−, SO4 2−, NO3 −, Br−, and I− in the basic pH range

Sorption of arsenate by stannum(IV)-exchanged zeolite P

Zeolites are crystalline, hydrated aluminosilicate containing exchangeable alkaline and alkaline earth cations in their structural frameworks. Previous studies have shown that modification of zeolites with an active metal cations yield sorbents with a strong affinity for certain anions. Recently hydrous tin oxide was found effective to remove arsenic anions from aqueous solution. In this study, sodium ion of zeolite P was exchanged with stannum(IV) and used for sorption of arsenate (As(V)) ion. Among parameters investigated were effect of pH, As(V) initial concentrations, contact time, temperature and effect of foreign ions. The results show that As(V) sorption by stannum(IV) exchanged zeolite P (SnZP) was maximum at about pH 2. The sorption capacities increase with increasing initial As(V) concentrations and follows Langmuir model with maximum sorption capacity of 83.33 mg/g at 25°C. The sorption capacity of As(V) by SnZP increased as temperature increases from 25 to 70°C showing that the process is endothermic with DH° value of 83.84 kJ mol-1. The free energy change (DG°) for the sorption was negative showing that the sorption of As(V) ions is spontaneous. The kinetics study shows that the As(V) sorption follows second order kinetic model. The free energy (E) was 12.91 kJ mol-1 which shows the sorption is an ion-exchange process. The As(V) sorption by SnZP was not affected by the presence sulphate, chloride, nitrate and carbonate but was significantly reduced by phosphate

Synthesis of Cuo and Zno nanoparticles and Cuo doped Zno nanophotocatalysts

Nanocrystalline copper oxide (CuO) particles were precipitated by using different sources of copper salts and oxalic acids. The transformation to monoclinic CuO is achieved by heating the copper precipitate at 300°C for 4 h. Dice-like and flower-like structures were obtained from the effects of by-product’s acidity to the morphology of copper oxalate (Cu (C2O4)). The particle sizes of all samples, determined by transmission electron microscopy (TEM), were in the range of 10-30 nm. 0.5% CuO doped ZnO (CuO-ZnO) nanophotocatalysts were successfully prepared by mixing synthesized CuO nanoparticles with synthesized ZnO in absolute methanol. No significant changes in morphology were observed between the undoped and doped ZnO except for a higher surface area obtained for CuO doped ZnO. The doping of CuO on ZnO also resulted in enhanced photocatalytic performance of ZnO in the photodegradation of methyl orange dye

Removal of Cu and Pb by tartaric acid modified rice husk from aqueous solutions

A study on the modification of rice husk by various carboxylic acids showed that tartaric acid modified rice husk (TARH) had the highest binding capacities for Cu and Pb. The carboxyl groups on the surface of the modified rice husk were primarily responsible for the sorption of metal ions. A series of batch experiments using TARH as the sorbent for the removal of Cu and Pb showed that the sorption process was pH dependent, rapid and exothermic. The sorption process conformed to the Langmuir isotherm with maximum sorption capacities of 29 and 108 mg/g at 27±2 °C for Cu and Pb, respectively. The uptake increased with agitation rate. Decrease in sorbent particle size led to an increase in the sorption of metal ions and this could be explained by an increase in surface area and hence binding sites. Metal uptake was reduced in the presence of competitive cations and chelators. The affinity of TARH for Pb is greater than Cu

Kinetics and thermodynamic for sorption of arsenate by lanthanum-exchanged zeolite

Zeolites are crystalline, hydrated aluminosilicate containing exchangeable alkaline and alkaline earth cations in their structural frameworks. Since zeolites have permanent negative charges on their surfaces, they have no affinity for anions. However recent studies have shown that modification of zeolites with certain surfactants or metal cations yield sorbents with a strong affinity for many anions. In this paper, modification of zeolites (zeolite A, X and ZSM5) were performed by exchange of naturally occurring cations with lanthanum ion that forms low solubility arsenate salt. The exchanged zeolites were used to sorb arsenate from aqueous solution. Among parameters investigated were effect of pH, arsenate initial concentrations, contact time and temperature. The maximum exchanged capacity of La(III) ion was obtained when using solution with initial pH of 4. Zeolite X gives the highest La(III) exchanged capacity compared to other zeolites. The results showed that As(V) sorption by La-zeolites occurred at about pH 6.5 and increased as pH increased and reaching maximum at equilibrium pH about 7.8. On the other hand, almost no arsenate sorption occurred on unexchanged zeolites. This indicates that La(III) ion on the exchanged zeolites is taking part on the As(V) sorption via surface precipitation. The results also showed that the sorption capacities increased with increasing initial As(V) concentrations. The sorption followed Langmuir model with maximum sorption capacities of 0.41, 0.21 and 0.19 mmol/g at 25°C for La exchanged zeolite X (La-ZX), La exchanged zeolite ZSM5 (La -ZSM) and La exchanged zeolite A (La-ZA), respectively. The amo unts of sorption of As(V) by La exchanged zeolite increased as temperature increased from 25 to 70°C indicating that the process is endothermic. The free energy changes (DG°) for the sorption at 25°C were -10.25, -9.65 and -8.49 kJ/mol for La-ZX, La -ZSM and La-ZA, respectively. The negative values of DG° meant that the sorption of As(V) ions on La-exchanged zeolite was spontaneous, perhaps because the La(III) had high affinity towards the arsenic ion as indicated by a low Ksp value of of lanthanum arsenate. A slightly positive entropy change for sorption of As(V) ion on La-exchanged zeolite could be due to fixation of the ions on the La(III) exchange sites that was randomly distributed on the sorbents. The kinetics study showed that the As(V) sorption followed first order kinetic model. The first-order kinetic constants for the sorption are 2.77x10-3, 2.25x10-3 and 1.60x10-3 min-1 for La-ZX, La -ZSM and La-ZA, respectively

Effects of copper overload on hepatic lipid peroxidation and antioxidant defense in rats

The influence of copper (Cu) overload on hepatic lipid peroxidation and antioxidation defense capacity was studied by overloading rats with copper sulphate orally (500 mg Cu/kg bw) 5 d/w for 8 w. Malondialdehyde (MDA), Cu-Zn superoxide dismutase (SOD), and Se-glutathione peroxidase (GSH-Px) were measured in serum and liver homogenate at 2, 4 and 8 w of dosing. Liver Cu concentration and alanine aminotransferase (ALT) activity were also determined. As Cu loading progressed, there were multiparameter changes with significant ALT elevation, increased MDA concentrations in serum and liver homogenate, and dramatic declines of SOD and GSH-Px activities in erythrocytes and whole blood respectively, along with marked elevation of hepatic Cu in the Cu-dosed group. Excessive Cu accumulation in the liver depressed SOD and GSH-Px activities and resulted in high MDA in serum and liver homogenate due to the lipid peroxidation induced by the Cu overload