Production of biosorbents from waste olive cake

The atmosphere has become a major pathway for long-range transfer of Cr to different ecosystems. The wind carries atmospheric Cr-containing particles over different distances, before they fall or are washed out from the air onto the terrestrial and water surfaces. Meteorological factors, topography and vegetation as well as particle size influence the distance covered by the metal . Speciation of Cr is less important in this transportation system. Transport within the terrestrial and water systems instead is greatly affected by chemicalspeciation: the biogeochemical cycle of this element is determined by chemical forms of Cr and their affinity to chemical and photochemical redox transformations, precipitation/dissolution and adsorption/desorption processes occurring in individual compartments of the environment. The effect of atmospheric input of Cr is limited by the efficient adsorption of metals by soils. Cr(III) is generally not transported over great distances due to its low solubility and tendency to be adsorbed in the pH range typical for natural soils and waters. Cr dislocation from the soil into the water system can be increased by the oxidation of Cr(III) to the mobile form Cr(VI). Also the soluble Cr(III) complexed by discrete organic ligands can be transported to groundwater and within the water systems. The transport mechanism of metals in rivers is associated mostly with suspended particles. In the ocean and sea waters the precipitated and dissolved Cr exist in equilibrium. Dissolved Cr is lost from the oceanic water column through incorporation into biologic material, mainly siliceous and carbonaceous skeletons, and adsorption onto sediment particles. In anoxic basins and the oxygen-free zones, where reduction of hexavalent Cr occurs, increased Cr removal may be due to Cr(III) adsorption onto bottom sediments. The
remobilization of Cr(III) from sediment can also occur by its oxidation, carried out mostly by manganese dioxide. In lakes, the high level of organic matter favors Cr(VI) reduction to Cr(III), which is afterwards rapidly precipitated or adsorbed onto the sediment minerals. Remobilization into the surrounding pore water may occur via oxidation or solubilization of Cr(III) precipitates. Also, the oxygenated medium favors Cr(VI), whereas under anoxic conditions, Cr(III) is being produced followed by particle scavenging.Biomass can also play a role in Cr transport. In oceans, plankton may absorb some part of this metal. Further, it can be flocculated with faecal pellets or dead organisms and become incorporated into sediment instead of being transported. But, within food webs Cr transport does not result in any major quantitative relocation, since the proportion of the metal content of the ecosystem that is removed or introduced by organisms is usually small. Again, the hexavalent anionic form is more available for living organisms than is trivalent Cr, and plays a main role in removing this metal from water and soil systems.