1. E. Fosso-Kankeu, C.M. Van der Berg, F.B. Waanders, Physico-chemical activation of South African bentonite clay and impact on metal adsorption capacity, 6th International Conference on Green Technology, Renewable Energy and Environmental Engineering (ICGTREEE’2014), 27–28 November 2014, Cape Town-South Africa, E. Muzenda, S. Sandhu, eds., (2014) pp 247–252.
  2. K.G. Bhattacharyya, S.S. Gupta, Adsorptive accumulation of Cd(II), Co(II), Cu(II), Pb(II), and Ni(II) from water on montmorillonite: influence of acid activation, J. Colloid Interface Sci., 310(2) (2007) 411–424.
  3. Q. Cheng, C. Wang, K. Doudrick, C.K. Chan, (2015) Hexavalent chromium removal using metal oxide photocatalysts, Appl. Catal. B: Environ., 1(177) (2015) 740–748.
  4. L. Hu, Y. Cai, G. Jiang, Occurrence and speciation of polymeric chromium (III), monomeric chromium (III) and chromium (VI) in environmental samples, Chemosphere, 156 (2016) 14–20.
  5. T. Santonen, A. Zitting, V. Riihimaki, P.D. Howe, M. Wood, Concise International Chemical Assessment Document 76: Inorganic Chromium (III) Compounds (2009).
  6. D. Metze, N. Jakubowski, D. Klockow, Speciation of chromium. In: R. Comelis, H. Crews, J. Caruso, K.G. Heumann, eds., Handbook of Elemental Speciation II: Speciation in the Environment, Food, Medicine & Occupational Health. John Wiley & Sons, Ltd (2005).
  7. M.A. Stewart, P.M. Jardine, M.O. Barnett, T.L. Mehlhorn, L.K. Hyder, L.D. McKay, Influence of soil geochemical and physical properties on the sorption and bioaccessibility of chromium (III), J. Environ. Qual., 32 (2003) 129– 137.
  8. IARC, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, vol. 49. Chromium, Nickel and Welding, 1990.
  9. WHO, Chromium in drinking-water. Background Document for Preparation of WHO Guidelines for Drinking-water Quality, World Health Organization, Geneva, (WHO/SDE/WSH/03.04/4) (2003).
  10. E. Peterson-Roth, M. Reynolds, G. Quievryn, A. Zhitkovich, Mismatch repair proteins are activators of toxic responses to chromium-DNA damage, Mol. Cell. Biol., 25 (2005) 3596–3607.
  11. A. Leonard, R.R. Lauwerys, Carcinogecity and mutagenicity of chromium, Mutat. Res. Rev. Genet., 76 (1980) 227–239.
  12. F. Majone, and A.G. Levis, Chromosomal aberrations and sister-chromatid exchanges in chinese hamster cells treated in vitro with hexavalent chromium compounds, Mutat. Res. Rev. Genet. Toxicol., 67 (1979) 231–238.
  13. T. Fang, X. Yang, L. Zhang, J. Gong, Ultrasensitive photoelectrochemical determination of chromium (VI) in water samples by ion-imprinted/formate anion-incorporated graphitic carbon nitride nanostructured hybrid, J. Hazard. Mater., 312 (2016) 106–113.
  14. R. Donat, A. Akdogan, E. Erdem, H. Cetisli, Thermodynamics of Pb2+ and Ni2+ adsorption onto natural bentonite from aqueous solutions, J. Colloid Interface Sci., 286(1) (2005) 43–52.
  15. Z. Orolínová, A. Mockoviaková, Structural study of bentonite/iron oxide composites, Mater. Chem. Phys., 114(2–3) (2009) 956–961.
  16. Y. Chen, Adsorption of La(III) onto GMZ bentonite: effect of contact time, bentonite content, pH value and ionic strength, J. Radioanal. Nucl. Chem., 3(292) (2012) 1339–1347.
  17. T.S. Anirudhan, M. Ramachandran, Adsorptive removal of basic dyes from aqueoussolutions by surfactant modified bentonite clay(organoclay): Kinetic and competitive adsorption isotherm, Process Saf. Environ. Prot., 1(95) (2015) 215–225.
  18. D.J.L. Guerra, I. Mello, L.R. Freitas, R. Resende, R.A.R. Silva, Equilibrium, thermodynamic, and kinetic of Cr(VI) adsorption using a modified and unmodified bentonite clay, Int. J. Mining Sci. Tech., 1 (24) (2014) 525–535.
  19. C. Yong-Gui, H. Yong, Y. Wei-Min, J. Ling-Yan, Competitive adsorption characteristics of Na(I)/Cr(III) and Cu(II)/Cr(III)on GMZ bentonite in their binary solution, J. Ind. Eng. Chem., 1(26) (2014) 335–339.
  20. X. Shuibo, Z. Chun, Z. Xinghou, Y. Jing, X. Zhang, W. Jingsong,Removal of uranium (VI) from aqueous solution by adsorption of hematite, J. Environ. Radioact., 1 (100) (2009) 162–166.
  21. A. Dimirkou, A. Loannou, N. Doula, Preparation, characterization and sorption properties for phosphates of hematite, bentonite and bentonite–hematite systems, Adv. Colloid Interface Sci., 1 (97) (2002) 37–61.
  22. Z.-H. Ruan, J.-H. Wu, J.-F. Huang, Z.-T. Lin, Y.-F. Li, Y.-L. Liu, P.-Y. Cao, Y.-P. Fang, J. Xie, G.-B. Jiang, Facile preparation of rosin-based biochar coated bentonite for supporting α-Fe2O3 nanoparticles and its application for Cr(VI) adsorption, J. Mater. Chem. A., 3 (8) (2015) 4595–4603.
  23. X. Tan, Y. Liu, G. Zeng, X. Wang, X. Hu, Y. Gu, Z. Yang, Application of biochar for the removal of pollutants from aqueous solutions, Chemosphere, 125 (2015) 70–85.
  24. A. Liu, Y. Park, Z. Huang, B. Wang, R.O. Ankunah, P.K. Biswas Product identification and distribution from hydrothermal conversion of walnut shells, Energ. Fuels, 20 (2006) 446–454.
  25. Y. Yao, B. Gao, J. Fang, M. Zhang, H. Chen, Y. Zhou, A.E. Creamer, Y. Sun, L. Yang, Characterization and environmental applications of clay–biochar composites, Chem. Eng. J., 242 (2014) 136–143.
  26. S. Wang, B. Gao, Y. Li, A. Mosa, A.R. Zimmerman, L.Q. Ma, W.G. Harris, K.W. Migliaccio, Manganese oxide-modified biochars: Preparation, characterization, and sorption of arsenate and lead, Bioresour. Technol., 181 (2015) 13–17.
  27. S. Wang, B. Gao, A.R. Zimmerman, Y. Li, L. Ma, W.G. Harris, K.W. Migliaccio, Removal of arsenic by magnetic biochar prepared from pinewood and natural hematite, Bioresour., Technol., 175 (2014) 391–395.
  28. Y. Lee, J. Park, C. Ryu, K.S. Gang, W. Yang, Y.-K. Park, J. Jung, S. Hyun, Comparison of biochar properties from biomass residues produced by slow pyrolysis at 500°C, Bioresour. Technol., 148 (2013) 196–201.
  29. E. Fosso-Kankeu, A.F. Mulaba-Bafubiandi, B.B. Mamba, T.G. Barnard, Prediction of metal-adsorption behaviour in the remediation of water contamination using indigenous microorganisms, J. Environ. Manage., 92(10) (2011) 2786–2793.
  30. H. Mittal, E. Fosso-Kankeu, S.B. Mishra, A.K. Mishra, Biosorption potential of Gum ghatti-g-poly (acrylic acid) and susceptibility to biodegradation by B. subtilis, Int. J. Biol. Macromol., 62 (2013) 370–378.
  31. E. Fosso-Kankeu, H. Mittal, S.B. Mishra, A.K. Mishra, Gum ghatti and acrylic acid based biodegradable hydrogels for the effective adsorption of cationic dyes, J. Ind. Eng. Chem., 22 (2015) 171–178.
  32. R. Yin, R. Liu, Y. Mei, W. Fei, X. Sun, Characterization of bio-oil and bio-char obtained from sweet sorghum bagasse fast pyrolysis with fractional condensers, Fuel, 112 (2013) 96–104.
  33. B.S. Al-Farhan, Potential removal of crystal violet (CV), acid red (AR) and methyl orange (MO) from aqueous solution by magnetic nanoparticles, Int. J. Nanomater. Chem., 1(3) (2015) 97–102.
  34. Y. Sag, B. Akeael, T. Kutsal, Ternary biosorption equilibria of Cr(VI), Cu(II) and Cd(II) on Rhizopus arrhizus, Sep. Sci. Technol., 37 (2002) 279–309.
  35. M. Lawrinenko, Anion exchange capacity of biochar. Thesis in Master of Science at the Iowa State University, Department of Agronomy, (2014).
  36. H.I. Adegoke, F. AmooAdekola, O.S. Fatoki, B.J. Ximba, Adsorption of Cr(VI) on synthetic hematite (α-Fe2O3) nanoparticles of different morphologies, Sep. Technol. Thermody., 31(1) (2013) 142–154.
  37. A.O. Dada, J.O. Ojediran, A.P. Olalekan, Sorption of Pb2+ from aqueous solution unto modified rice husk: Isotherms studies, Adv. Phys. Chem., (2013) 1–6.