The flotation of Strontium ions from aqueous solutions has been investigated using cetyl trimethyl ammonium bromide, potassium laurate, sodium lauryl sulphate or Aerosol 18 as collector. Aerosol 18 proved to be the most suitable. With this reagent Strontium removals of about 97.5% 99% could be achieved for metal ion concentrations ranging from 1 X 10\"' M (or probably less) to 1.3X 10\"\" M. The effectsof pH, collector concentration, ionic strength, gas flow rate and period of bubbling were determined and the optimum flotation conditions have been established.

The Removal of Radioactive Strontium from Aqueous Solutions by Foam Separation

Numerous techniques are available for the separation of homogeneous liquid mixtures. These include such classical methods as distillation, extraction and adsorption. In general, separation efficiencies decrease rapidly as the concentration of the desired component falls off. Ion exchange and selective adsorption, as well as some of the newer techniques, have found applicability in the low concentration range. Similarly, foam separation is a “low concentration” technique. On a commercial scale, the method has been proposed and studied in the area of sewage treatment, recovery and/ or decontamination of nuclear wastes, and recovery of values from sea water. Although foam separation has been a subject of study in the laboratory for well over 50 years, i t is a relatively unknown technique. I ts potential applicability as a general separation and purification tool remains to be demonstrated. One of the objectives of this paper is to summarize the state of the art of foam separation so that it may be placed in proper perspective relative to the many other available separation and purification techniques. Foam separation is a technique utilizing stable foams to separate componentsin solution. I t is based upon the tendency of surface active solutes to collect a t the gas-liquid interface. Foaming is simply a practical means of producing and collecting large quantities of gas-liquid interface. The technique is superficially similar to froth flotation procedures used in mineral beneficiation. The two are entirely different in principle. Foam separation is used with true solutions or colloids, while froth flotation involves removal of solids-in-suspension. Foam separation has long been known for concentrating surface active components in the foam phase. This was of limited interest as a separation technique. In 1957 it was found that metal ions in solution could also be separated by the addition of surface active agents capable of complexing the metal ions and carrying them along to the gas-liquid interface. Choice of foaming agent, as well as operating parameters, permitted selective separation of metal ions from one another.

Foam separation as a purification and preparative tool

The removal of cesium, strontium, and rare earth cations from dilute aqueous solutions by adsorption on foam surfaces was studied. The primary objective in the study was to determine the technical feasibility of a foam separation process for the removal of specific nuclides from nuclear process streams. Foam separation takes advantage of the concentration difference existing between the surface layers and the bulk regions of solutions containing surface active solutes. Enrichment of non-surface active materials, such as cations and arions, at the air-water interface may be achieved by complexing these materials into a surface active form. Equilibrium surface adsorption coefficients, GAMMA /C, were determined for cesium, strontium, and samarium in 10/sup -5/M solutions combined with various surface active agents. Among those studied, the foaminB agents that showed best selectivity for strontium and samarium were the amino polycarboxylic acids. Promising cesium enrichments were obtained using a combination of an amino polycarboxylic acid and sodium tetraphenyl boron. The equilibrium surface adsorption was found to depend upon the type of foaming agent, the foaming agent concentration, the metal non concentration, pH, the inert salt (NaNO/sub 3/) concentration, and the temperature. Continuous separation of strontium and samarium from 10/sup -5/M aqueous solutions containing lMmore » sodium nitrate was studied in experimental countercurrent foam columns. Decontamination values of 400 to 7OO were demonstrated for strontium and samarium in a single pass through a three foot foam column, with corresponding volume reductions of 100 to 400 without evaporation. Decontamination values for strontium in the order of 10/sup 4/ to lO/sup 7/ were observed in a four column series set up. A study of the effect of the continuous column operating variables, such as liquid and gas flow rates, foam bubble size, column dimensions and temperature, on the separation efficiency was conducted. It was concluded that the degree of metal ion separation is primarily dependent on three factors: the equilibrium distribution coefficient, the ratio of the surface area generated to the liquid feed rate, and the height of the foam column. The experimental results indicate that the performance of a continuous countercurrent foam column can be quantitatively described by a Kremser or Colburn type of relationship, commonly employed in the design of conventional mass transfer unit operations. Relationships of this type were derived from a mathematical analysis of a foam column model. (auth)« less

R. Sanford

Papers

THE REMOVAL OF STRONTIUM AND CESIUM FROM NUCLEAR WASTE SOLUTIONS BY FOAM SEPARATION. Final Report