Risto Koivula

Purification of metal plating rinse waters with chelating ion exchangers

A wide range of chelating ion exchangers was tested for their abilities to remove Zn, Ni, Cu and Cd from solutions simulating waste effluents from the metal-plating industry. The task was to reduce metal discharges to the environment so that metal-plating shops could keep up with the modern, more stringent regulations of waste effluents. The resins were tested by batch and mini-column experiments. Decontamination factors (DFs) as high as 700 and capacities up to 3.3 meq/mL were measured at the 5% breakthrough (BT) point in mini-column tests. Complexing agents, especially cyanide, considerably reduced the performance of the resins with only a few exceptions. Ammonium seemed to improve the ion-exchange performance of some chelating resins and capacities higher than the theoretical values, given by the manufacturer, were measured. Comparative experiments between chelating, strong acid and weak acid ion-exchange resins showed that the advantage of chelating exchangers over strong and weak acid exchangers is a very low metal BT level, even as low as 2 μg/L, which is very important, especially in the end-of-pipe polishing.

Capture of Co(II) from its aqueous EDTA-chelate by DTPA-modified silica gel and chitosan

The adsorption of Co(II) by diethylenetriaminepentaacetic acid (DTPA)-modified silica gel and chitosan in the presence of EDTA and other interfering species was studied. Co(II) removal ranged from 93% to 96% from the solutions where Co(II) was totally chelated by EDTA. The amount of oxalate or Fe(II) did not affect the adsorption of Co(II) in the case of DTPA-chitosan. However, increasing the amount of oxalate enhanced the adsorption performance of DTPA-silica gel, probably due to the formation of new active sites on the silica gel surface. DTPA-chitosan was also effective in simulated decontamination solutions. For DTPA-silica gel, the rate of adsorption of free Co(II) was controlled by pore diffusion, but the rate of adsorption of Co(II)EDTA was controlled by the surface chelation reaction, which was attributed to the inhibited diffusion of Co(II)EDTA inside the silica gel mesopores. However, the macroporous structure of DTPA-chitosan enabled pore diffusion of both Co(II) and Co(II)EDTA. The equilibrium isotherms of DTPA-silica gel were best described by a BiLangmuir model, in which there are two different adsorption sites on the silica gel surface assigned to different speciations of DTPA. For DTPA-chitosan, the data fit best with a Sips model, which indicates system heterogeneity. Finally, measurements with capillary electrophoresis showed an increase in dissolved EDTA during adsorption, demonstrating the ability of DTPA-modified adsorbents to release Co(II) from its EDTA chelate. This promising result can provide a basis for applying the studied materials to the treatment of water effluents containing Co(II) chelated by EDTA by a simple one-step adsorption process.

Nanoporous manganese oxides as environmental protective materials-effect of Ca and Mg on metals sorption.

The selectivity of nanoporous manganese oxides for some alkali and transition metals over calcium and magnesium was studied. Two tunnel-structured oxides (OMS-1 and OMS-2) were synthesized by means of a hydrothermal route. Competitive uptake of metals and acid was studied using batch kinetic measurements at different metal ion concentrations. The experimental data were correlated with a dynamic model. The results show that the studied OMS materials selectively adsorb Cu, Ni and Cd in the presence of Ca and Mg. It was also found that the exchange rates were reasonably high due to the small particle dimensions. Both materials are stable in the studied conditions and their maximum Cu uptake capacity was 0.9-1.3 mmol/g. The results indicate that both materials have potential for environmental applications involving the uptake of harmful metal ions.

Sorption of radiocobalt and its EDTA complex on titanium antimonates

The sorption properties of two synthesized titanium antimonate materials were tested in simulated nuclear power plant decontamination solutions. The aim was the removal of radiocobalt in the presence of complexing agents such as EDTA and oxalate. The first titanium antimonate material had a mixture of pyrochlore and rutile structures and it showed good tolerance for the complexing agents. 91% of cobalt was removed in the presence of EDTA, and oxalic acid had only a minor effect on the sorption. The other material, which had a mopungite structure, tolerated EDTA well (97% removal of cobalt) but its sorption properties for cobalt were restricted to a specific amount of oxalic acid. The sorption efficiency of cobalt increased for both materials when the cobalt concentration was less than 1 microM, indicating that the synthesized materials are efficient sorbents, especially for trace amounts of radiocobalt.

The effect of dopant’s valence (+III and +V) on the anion/cation uptake properties of antimony-doped tin dioxide

Antimony is perhaps the most frequently used doping element of tin dioxide. Although antimony of different oxidation states have been used in the synthesis, the effect of dopant’s valence on ion exchange properties has not been investigated critically. In our study the valence of antimony had clear effects on the metal uptake properties of Sb-doped SnO2 materials. Extremely high Tc uptake (Kd > 100 000 mL g−1) on Sb(III)-doped material was observed in conditions under which Sb(V)-doped material did not show any Tc uptake. However, the Sb(V)-doped material showed good Ni2+ uptake properties (Kd up to 33 000 mL g−1), even at pH values below the material’s point of zero charge (pzc), while the Sb(III)-doped material showed Ni2+ uptake only at pH above its pzc. The cation uptake of Sb-doped SnO2 resembles typical weakly acidic cation exchanger character but the uptake of TcO4- does not follow a typical anion exchange pattern. Instead, we propose a sorption process related to redox reactions as the probable Tc uptake process.

Selective Sorption of Technetium on Antimony-Doped Tin Dioxide

Glassy, nanocrystaline antimony-doped hydrous tin dioxide was alkali precipitated from acidic metal chloride solution. The material has good thermal stability and granular physical form that enables its use in a conventional column. The material shows excellent, almost quantitative, uptake properties for 99Tc radionuclide. Its distribution coefficients (Kd values) for 99Tc were typically over 1 000 000 (ml/g) in solutions of one molar ionic competition (at neutral pH) and the uptake remained high over a broad pH range (2-11). By comparison, conventional cation/anion resins yielded Kd values of less than 200. The Tc uptake mechanism of antimony-doped tin dioxide is most likely a sorption process that cannot be categorized as typical cation or anion exchange. Redox reactions between Tc and Sb were speculated as being the phenomenon. Thermal treatment increased the materials crystal size from amorphous to ∼15 nm and changes in the oxidation state of antimony from +3 to +5 occurred at temperatures above 400°C. Also, the materials Tc uptake properties were increased by the thermal treatment.

Behavior of Silica-Supported Manganese Oxides in Hydrometallurgical Separations

Abstract The properties of nanoporous manganese oxides for metal uptake from hydrometallurgical solutions were studied. Layer-structured OL-1 and tunnel-structured OMS-1 were synthesized by means of a hydrothermal route and then supported on silica. Competitive uptake of metals and acid was studied using equilibrium, batch kinetic, and fixed-bed measurements. The experimental data were correlated with a dynamic model, which also accounts for the dissolution of the framework manganese. Results show that silica–supported OMS materials can be utilized to separate copper from nickel and cadmium. Behavior of the composites can be explained reasonably well with the presented model and the parameters estimated from the data of the unsupported oxides.

The effect of 0–100% Sn/Sb substitution on nickel uptake of tin antimonates

The nickel uptake properties of an extensive series of tin antimonates were studied. Distribution coefficient values (Kd) for 63Ni were measured in acidic and calcium solutions and illustrated as a function of Sn/Sb substitution from 0 to 100%. High Kd values for nickel from acidic solution (0.1 M HNO3) were obtained, and Kd values from 0.1 M Ca(NO3)2 solution followed in a similar manner but at a considerably lower level. It was suggested that the nickel uptake was governed by structural hindrance in the pyrochlore phase and by electrostatic forces in the rutile phase. The dependence of pH on nickel uptake from floor drain water simulate was investigated using three materials with different Sn/Sb ratios, and excellent Kd values, even over 175 000 ml g−1, were obtained.

Separation of Europium from Cobalt Using Antimony Silicates in Sulfate Acidic Media

The ores of rare earth elements (REEs) are usually digested in concentrated sulfuric acid media, which dissolve the REEs as main product with heavy metals as byproduct. In the present work, inorganic ion exchangers based on silico-antimonates (SiSb) were synthesized and characterized. SiSb mixed with metal oxides were prepared in molar ratio 2:1 with different aging time. In batch experiments, radionuclides Eu-152 and Co-57 were taken to represent the lanthanides and heavy metals, respectively. The sorption behavior was examined and distribution coefficients were evaluated for different effective conditions such as sulfuric acid concentration, pH, shaking time, metal ion concentration, and aging time. The new inorganic SiSb materials are characterized by rapid kinetics for Eu(III) and high adsorption selectivity for Co(II). The results showed that the SiSb are acidic in character and that their cation-exchange properties are better in low acidic media. Sorption efficiency is highly correlated with the structural framework, which depends on exchangeable water content. Various chelating agents were tested for desorption of the retained Eu(III) and Co(II). Maximum separation factors were obtained with SiSb materials after 2 or 3 days aging, providing efficient exchangers for the separation of economically valuable REEs from heavy metals.

63Ni and 57Co uptake and selectivity of tin antimonates of different structure

Tin antimonates of different structure were studied for their uptake of cobalt and nickel in the decontamination of floor drain water and neutral bond water simulates. Selectivity was observed to vary with the structures and degree of crystallinity of the tin antimonates (pyrochlore, rutile, and mixed metal oxides). High selectivity for cobalt of exchangers with pyrochlore structure is attributed to ion exchange of cobalt inside the tunnel structure; nickel uptake evidently took place mostly at the outer surfaces of the materials. Electrostatic forces governed the ion exchange of rutile tin antimonates owing to their particle hydrate structure. With some limitation, the prediction of nickel uptake on tin antimonates from the more abundant cobalt uptake data is considered possible.