Adsorption of cesium, strontium, and cobalt ions on magnetite and a magnetite-silica composite

Constant pH adsorption isotherms for nonradioactive Cs+, Sr2+, and Co2+ On pure magnetite and a 80% (w/w) magnetite-silica composite were measured at 25 degreesC over a wide range of metal ion concentrations. The adsorption studies were carried out at four different pH's: 6, 7, 8, and 9 for Cs+ and Sr2+ and 5, 6, 7, and 8 for Co2+. All of the constant pH isotherms exhibited type I behavior with a saturation capacity that was pH-dependent and increased with increasing pH. The corresponding distribution coefficients increased with increasing pH but decreased with increasing metal ion concentration; they were also 10-1000 times lower than those reported in the literature for more selective but more expensive adsorbents. These two magnetite-based adsorbents also exhibited moderate regeneration conditions, with nearly 90-100% regeneration achieved in most cases at pH values between 1 and 3. A Langmuir model with pH-dependent parameters was also fitted successfully to all of the constant pH adsorption isotherms. This experimental data and the corresponding pH-dependent Langmuir correlation should find considerable use in the design and development of inexpensive fixed-bed adsorption processes for the removal of the radioactive isotopes of Cs+, Sr2+, and Co2+ from aqueous solutions that are produced in nuclear facilities. Magnetite, when encased in silica and placed in a packed column, can also be used as the charging element in high gradient magnetic separation, thereby removing not only metal ions via surface complexation (adsorption) but also nanoparticles of a paramagnetic nature.