Adsorption of Cesium, Strontium, and Cobalt Ions on Magnetite and a Magnetite−Silica Composite

• Published in: Industrial & engineering chemistry research Vol. 40; no. 7; pp. 1615 - 1623
• Main Authors: Ebner, Armin D, Ritter, James A, Navratil, James D
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 04.04.2001
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Solid-liquid interface; Surface physical chemistry; Metallic adsorbate; Correlation; Liquid solid interface; Liquid solid adsorption; Liquid solid desorption; Adsorption isotherm; Adsorption capacity; Metal ion; Partition coefficient; Inorganic adsorbent; Experimental study; Silica; Composite material; Alkaline earth metal Ions; Transition metal Ions; Magnetite; Medium effect; Cesium Ions; Concentration effect; Alkali metal Ions; Cobalt II Ions; pH; Strontium Ions; Aqueous solution
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie000695c

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 °C 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.