Evaluation of synthetic Birnessite utilization as a sorbent for cobalt and strontium removal from aqueous solution M. Ghaly a , Farida M.S.E. El-Dars b , M.M. Hegazy b , R.O. Abdel Rahman a,⇑ a Hot Laboratory Center, Atomic Energy Authority of Egypt, P.O. 13759, Inshas, Cairo, Egypt b Chemistry Department, Faculty of Science, Helwan University, Ain Helwan, 11795 Cairo, Egypt highlights  Prepared Birnessite has good sorptive behavior and thermal and chemical stability.  Contaminants are removed as CoCl + through chemical reaction and Sr 2+ via H-bond.  Empirical model was deduced to correlate the removal with time and temperature.  Transient removal mechanism obey mechanistic double-diffusive-barrier model. article info Article history: Received 4 July 2015 Received in revised form 1 September 2015 Accepted 2 September 2015 Available online 16 September 2015 Keywords: Birnessite Kinetics Modeling Radioactive waste Removal abstract Remediating aqueous solution contaminated by cobalt and strontium using synthetic Birnessite was investigated. Birnessite structure and chemical properties were evaluated; the material belongs to K-Birnessite family with alternate triclinic and hexagonal layers, where water molecules and potassium ions are interlaced between MnO layers. It is thermally stable and chemically very stable at slightly acidic conditions (pH = 5), and its stability under slightly acidic to alkaline conditions (5 = pH < 10) is higher than that of acidic media pH < 5. Equilibrium sorptive behavior was investigated by conducting batch experiments and modeling species distribution for these experiments to identify preliminary the geochemical suitability of Birnessite. The material remediates efficiently aqueous solutions (% uptake >90%) under acidic and slightly alkali conditions. The removal process is achieved by exchanging hydro- gen ions in the interlayer hydroxyl group and CoCl + or Sr 2+ species. Transient removal investigations were carried out and cobalt removal was found faster than strontium. The reaction is spontaneous, endother- mic and of increased disorder. The value of enthalpy change indicates that CoCl + is bonded to Birnessite via chemical reaction, where Sr 2+ is bonded via hydrogen bond in a double step reaction. Transient data analysis using rate models were used to deduce empirical equations for sorbed contaminants amounts as a function of contact time and ambient temperature. Transient removal mechanism was further investi- gated using double-diffusive-barrier model to identify the transport parameters through solid–liquid interface and bulk Birnessite particles. Reaction equilibrium isotherm follows Generalized Langmuir model and the sorbent has higher affinity to stabilize strontium. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Poor historical radioactive waste management and nuclear and radioactive accidents resulted in different contamination problems to soil, surface water and groundwater in different places around the world [1,2]. Remediating radioactive contaminated sites receives considerable attention due to several economical and ethical considerations. The managements of these sites are specific, i.e. dependent on the site characteristics, chemical and radiological characteristics of contaminants, land use and fund availability. Dif- ferent remediation technologies are available; the selection of appropriate technology is bonded by contamination characteris- tics, reliability, maturity and robustness of the technology, ease of maintenance, and ability to meet regulatory acceptance [3,4]. Chemical characteristics of contaminations vary from site to site depending on its source, but generally include alkali, alkaline earth, heavy metals, transition, and actinide elements [1,5,6]. Chemical stabilization is well developed technique to remediate http://dx.doi.org/10.1016/j.cej.2015.09.025 1385-8947/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +20 106140446. E-mail addresses: alaarehab@yahoo.com, karimrehab1@yahoo.com (R.O. Abdel Rahman). Chemical Engineering Journal 284 (2016) 1373–1385 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej