Studies were performed to determine the effect of pH on chromium (Cr) binding by native, esterified, and hydrolyzed saltbush (Atriplex canescens) biomass. In addition, X-ray absorption spectroscopy studies were performed to determine the oxidation state of Cr atoms bound to the biomass. The amounts of Cr adsorbed by saltbush biomass were determined by inductively coupled plasma–optical emission spectroscopy (ICP–OES). For Cr(III), the results showed that the percentages bound by native stems, leaves, and flowers at pH 4.0 were 98%, 97%, and 91%, respectively. On the other hand, the Cr(VI) binding by the three tissues of the native and hydrolyzed saltbush biomass decreased as pH increased. At pH 2.0 the stems, leaves, and flowers of native biomass bound 31%, 49%, and 46%, of Cr(VI), respectively. The results of the XAS experiments showed that Cr(VI) was reduced in some extend to Cr(III) by saltbush biomass at both pH 2.0 and pH 5.0. The XANES analysis of the Cr(III) reaction with the saltbush biomass parts showed an octahedral arrangement of oxygen atoms around the central Cr(III) atom. The EXAFS studies of saltbush plant samples confirmed these results.
The effect of pH on Cd(II) binding capacity of saltbush biomass was determined. Metal quantification performed using ICP/OES showed that Cd binding increased as pH increased from 2.0 to 5.0. The highest percentage of Cd bound ranged from 74-81%, 22-40%, and 70-80% for the native, esterified, and hydrolysed biomass. XAS studies showed that cadmium was present as Cd(II) and oxygen was the nearest neighbouring atom with bond lengths of approximately 2.3 Å and coordination numbers ranging between 4 and 5. Results indicated that carboxyl groups may be the primary ligand involved in the Cd binding by saltbush biomass.
EXAFS measurements have been performed from the Ge K edge and Bi LIII edge on GeSBi glasses with 6, 8 and 16 Bi at. %, and on crystalline Bi2S3. As expected, Ge is found to be fourfold coordinated with S atoms. It is also found that Bi is only coordinated with S with a coordination number CN = 4. This result for the CN of Bi contradicts the conclusion of Elliot and Steel. On the basis of the obtained CN of Bi, it is possible to exclude the presence of Bi2S3 microcrystalline inclusions and to assert that these glasses are homogeneous at the microscopic level.