The possibility to use the heterotrophic bacteria of Bacillus sp. for regeneration of natural montmorillonite and montmorillonite/iron oxide composite after the Cu(II) adsorption was studied and compared with the classical methods of chemical regeneration. After 10 days of bioleaching the bacteria released approximately 80% of loaded Cu(II), leaving the sorbents stable. Longer treatment and higher concentration of dissolved metal cations in the solution caused the reverse sorption of Cu(II) by

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... acteria. The treating of composite with adsorbed Cu(II) with organic acids (oxalic, citric) led to partial Cu(II) dissolution. The hydrochloric acid caused its structural destruction, liberated the Fe ions from the oxides precipitated on the bentonite surface. The bioregenerated sorbent was successfully repeatedly used for the Cu(II) adsorption.