Methylene blue was immobilized onto bentonite (BNT). The modified clay (MB-BNT) was used to extract Hg2+ at pH 6.0 yielding Hg-MB-BNT, BNT, MB-BNT and Hg-MB-BNT were characterized by X-ray diffractometry, infrared spectra, and elemental and thermogravimetric analyses. MB is suggested to be intercalated into the major phase of BNT; montmorillonite mineral (MMT), lying parallel to the aluminosilicate layers, with a capacity of 36 mequiv./100 g. MB-BNT shows good stability in 0.1-1 M hydrochloric or nitric acids, ammonium hydroxide, and concentrated Na+, K+ or NH4+ chlorides or iodides. It shows good selectivity towards Hg2+ with an extraction capacity of 37 mequiv./100g in the presence of I- giving rise to a ratio of MB/Hg2+/I- 1:1:3 in the clay phase. Extracted Hg2+ could be quantitatively recovered by ammonia buffer at pH 8.5. MB-BNT was successfully applied to recover Hg2+ from spiked natural water and cinnabar mineral samples using the optimum conditions; pH 6.0, time of stirring 10 min and 10 mL of 0.05 M NH4Cl/NH4OH at pH 8.5 as eluent. (C) 2010 Elsevier B.V. All rights reserved.