Intercalations of tetramethylammonium (TMA), tetraethylammonium (TEA), tetrapropylammonium (TPA), and tetrabutylammonium (TBA) ions into layered birnessite-type manganese oxide, BirMO(H), were studied in aqueous tetraalkylammonium hydroxide solutions with different concentrations. Expansions of the interlayer were not observed clearly in the TEA, TPA, or TBA systems. Stable colloidal suspensions were obtained in the TMA system at TAl/Hs (molar ratio of tetraalkylammonium ions over exchangeable protons in BirMO(H)) larger than 1. XRD analyses for these colloidal sediments in the wet state showed a short-range swelling by the TMA + intercalation, with an increase in the basal spacing (dbs) from 0.73 to 1.56 nm. The basal spacing decreased stepwise from 1.56 through 1.27 to 0.96 nm with a decrease of the relative humidity during drying. The chemical analysis results showed that the cation intercalation progressed by an ion exchange mechanism. The intrinsic selectivity coefficient for intercalation had a tendency to decrease with an increase in the ionic radius of guest cations, probably owing to the larger steric hindrance for larger ions. The intercalation of TBA + ions could be achieved by a two-step reaction involving treatment with (TMA)OH followed by (TBA)OH. The basal spacing increased from 1.56 to 2.19 nm due to the TBA + intercalation. No long-range swelling was clearly observed. However, delamination took place and the layered structure collapsed when TMA + -intercalated samples obtained at TAl/Hs ) 25 were washed with distilled water. Delamination was also observed in the washing of the TBA + -intercalated sample. Freeze-drying of the washed slurry gave a flakelike manganese oxide, which supports the finding of delamination in wet conditions. Upon air-drying, the reassembling of the manganese oxide sheet progressed and the amorphous phase reverted to the layered structure with basal spacing of 0.96 nm. The origins of short-range swelling and the delamination observed in the BirMO(H)-TMA + system are discussed in terms of attractive and repulsive forces by electrostatic interaction, hydration of interlayer cations, and interlayer hydrogen bonding.

Binding equilibria of a water-soluble chelating polymer, poly(acrylic acid), with divalent metal ions [Co(II), Ni(II), Cu(II), Zn(II), and Pb(II)] were measured by a batch ultrafiltration method in the pH range of 4-6. It was shown that the binding equilibrium curves were reasonably well represented by a complexation model accounting for the formation of three kinds of complexes [LM + , L 2 M, and L 2 M(HL) 2 ]. The equilibrium and successive stability constants were determined by fitting the binding curves calculated from the model to the experimental ones at every solution pH. The average coordination number was discussed on the basis of the complexation model proposed.

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The sufficient removal of heavy metals from sewage sludge remains to be achieved. Heavy metals that exist on the cell surfaces of the microorganisms in the sludge seem to be dissolved by acid treatments. This study shows that heavy metals in sewage sludge can be removed easily by treating a sludge filter cake with phosphoric acid containing hydrogen peroxide for 1 h at room temperature. Phosphoric acid of 8% concentration with hydrogen peroxide showed good removal rates of heavy metals comparable to those by 1 N hydrochloric acid. Copper is easily removed from the sludge in the presence of hydrogen peroxide. From the results of the investigation of the solubilities of several copper compounds into phosphoric acid with or without hydrogen peroxide, the copper in the sludge does not exist as copper sulfides, but it seems to exist as copper thiolates containing Cu(I) in biopolymers. In this process, the phosphoric acid used for the removal of heavy metals is almost entirely recovered and is reused. Sewage sludge with low content of heavy metals can be recycled as a useful resource.