Jukka Lehto

Removal of metals and anions from drinking water by ion exchange

Five organic and two inorganic ion exchangers were evaluated for the removal of metals and anions from water of two drilled wells. Sodium titanate (CoTreat) and a chelating aminophosphonate resin were the most efficient exchangers in removing transition metals from the total of 1800 bed volumes processed. CoTreat was the best for almost all of the transition metals. The breakthrough level of manganese was below 1% with CoTreat even when its concentration in the feed water was high (1 mg/l). The weak acid cation resin took up transition metals relatively efficiently. Somewhat unexpectedly, the cation exchangers also removed arsenic from water. Arsenic may have been sorbed on iron species, which again was adsorbed and filtered by the exchanger beds. Most of the cation exchangers took up calcium and magnesium at low processing capacities (<400 BV), and the strong base anion resin took up nitrate, bromide and sulphate very efficiently below 700 bed volumes. Neither chloride nor fluoride was taken up by the exchangers tested.

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.

Ion-exchange of nickel by iminodiacetic acid chelating resin Chelex 100

The distribution coefficient (KD) of trace nickel on an iminodiacetate-chelating resin Chelex 100 increased with pH to a peak value close to 2 000 000 ml/g at pH of about 5. At higher pH values the KD dropped to 5000 ml/g due to competition of an unidentified complexing agent. In equilibrium of three-component Na/H/Ni ion-exchange system, H/Ni exchange was found to be dominant in the pH range up to 8 and in Na concentration up to 6 mol/l. The practical ion-exchange capacity for nickel was 2.15 mmol/g (4.3 meq/g).

Selective Separation of Radionuclides from Nuclear Waste Solutions with Inorganic Ion Exchangers

Nuclear industry produces and stores large volumes of radioactive waste solutions. Removal of radionuclides from the solutions is an important and challenging task for two main reasons: reductions in the volumes of solidified waste, which have to be disposed of, and reductions in the radioactive discharges into the environment. Since the radioactive elements in most waste solutions are in trace concentrations and the waste solutions contain large excesses of inactive metal ions, highly selective separation methods are needed for the removal of radionuclides. A number of inorganic ion exchange materials are very selective to key radionuclides and they can play an important role in solving these problems. The spectrum of nuclear waste solutions is rather wide considering their radionuclide contents, concentrations of interfering salts and acidity/alkalinity. Therefore, several inorganic ions exchangers are needed for the removal of most harmful radionuclides from a variety of solutions. This paper discusses the use and requirements of inorganic ion exchange materials in nuclear waste management. Special attention is paid to the novel ion exchange materials developed in the Laboratory of Radiochemistry, University of Helsinki.

Absorption of cesium on potassium cobalt hexacyanoferrate(II)

Potassium cobalt hexacyanoferrate(II) was synthesized with a composition K1.70Co1.12Fe(CN)6 · 1H2O, a mixture of K2[CoFe(CN)6] (85–88%) and K2[CoFe(CN)6] (12–15%). Ion exchange was found to be stoichiometric, the exchangeable ions being potassium and cobalt in the ratios presented for the corresponding phases. The effective capacity for cesium was 0.35 meq/g, which is only 6% of the theoretical capacity. Cesium is probably only absorbed as a monolayer on the surface of the crystallites.

Industrial scale removal of cesium with hexacyanoferrate exchanger ― process development

An industrial scale process utilizing hexacyanoferrate-based ion exchangers was developed for the selective separation of radioactive cesium from nuclear waste solutions. This process was put into ...

Experimentation in ion exchange studies - the problem of getting reliable and comparable results

Abstract The experimental procedures for the determination of the most important equilibrium parameters of ion exchangers (ion exchange capacity, ion exchange isotherm, selectivity coefficient, distribution coefficient) are reviewed and discussed. Special emphasis is put on inorganic ion exchangers and ion exchange at trace concentrations. Experimental details that are sensitive for obtaining accurate and reliable equilibrium data are examined. In addition, the effects of physical and chemical phenomena that may distort the results of ion exchange equilibrium studies are examined and some guidelines are given on how to avoid these interferences.

Purification of metal finishing waste waters with zeolites and activated carbons

Sixteen zeolites and 5 activated carbons were tested for the removal of nickel, zinc, cadmium, copper, chromium, and cobalt from waste simulants mimicking effluents produced in metal plating plants. The best performances were obtained from 4 zeolites: A, X, L, and ferrierite types and from 2 carbon types made from lignite and peat. The distribution coefficients for these sorbents were in the range of 10,000-440,000 ml/g. Column experiments showed that the most effective zeolites for Zn, Ni, Cu, and Cd were A and X type zeolites. The activated carbons, Hydrodarco 3000 and Norit Row Supra, exhibited good sorption properties for metals in aqueous solutions containing complexing agents.

Separation of radioactive strontium from alkaline nuclear waste solutions with the highly effective ion exchanger SrTreat

SrTreat is an inorganic ion exchanger whose structure is based on a sodium titanate. It is available in granular form and is suitable for use in packed-bed operations. This exchanger has proved to be highly effective in the removal of radioactive strontium from alkaline nuclear waste solutions. SrTreat was used for the first time in an industrial-scale separation process in 1996 in Murmansk, Russia. During that operation 2500 bed volumes of low-active (22 kBq/) waste solution with a moderate salt concentration was decontaminated from 90 Sr with an average decontamination factor of 7400. The exchanger is especially suited for the decontamination of alkaline concentrated sodium nitrate solutions that are characteristic of neutralized stored wastes from some nuclear-fuel-reprocessing plants. At the Japanese Atomic Energy Research Institute (JAERI), a new radionuclide-removal system, successfully utilizing SrTreat for the removal of 90 Sr (7.4 GBq/) from a neutralized alkaline reprocessing waste solution, was commissioned in the summer of 1997. In the laboratory-scale tests with a JAERI simulant, adjusted to pH 10 and having 2.4 mol/ of NaNO 3 . strontium could be removed from more than 1000 bed volumes with an SrTreat column, thereby obtaining a decontamination factor between 2000 and 15 000. In addition to the performance of SrTreat columns in strontium removal, basic studies on the ion exchange equilibrium of strontium on SrTreat and the effects of pH and interfering cations on strontium exchange are discussed.

Purification of nickel and zinc from waste waters of metal-plating plants by ion exchange

Abstract A wide variety of chelating organic ion exchange resins and inorganic ion exchangers were tested for the removal of nickel and zinc from waste effluents from metal plating plants. Best performances were found to be exhibited by three chelating resins, sodium titanate and an active carbon impregnated with oxine. For most of these exchangers, the batch separation percentages were 99.9% or higher at pH above 5. Column experiments showed that the most effective exchanger for nickel was an inorganic ion exchanger, sodium titanate, and for zinc an aminophosphonate resin, Duolite ES 467.