Aluminum, sorption onto

Once they have reached higher pH, reducing conditions of the intestinal tract (Davis et al, 1992), sulhdes should be more stable, and may actually precipitate if reduced sulfur is present. Other solids, such as hydroxides or hydroxy-sulfates of aluminum, and possibly iron, may also precipitate. The increased pH should also lead to the increased sorption onto particulates of various metals and metalloids such as lead and copper (Smith, 1999). However, in vitro tests (Ruby et al, 1993) indicate that the increased complexing with unprotonated organic acids and enzymes helps offset the pH-driven precipitation and sorption of the base metals that were dominantly chloride-complexed in the stomach fluids. Arsenic and other oxyanionic species are likely to be sorbed as the stomach acids are neutralized, but may be partially desorbed once higher pH values are reached in the intestine (Ruby et al, 1996). 

Several hydrous oxides, such as those of aluminum, siTicon and, iron have been used to extract traces ions. Nevertheless, the sorption mechanism is not definitively established. Those oxides probably exhibit some ion exchange capacity among their properties and they can act as anionic or cationic exchangers and sometimes both. The separation of plutonium traces in the presence of HF by sorption onto an alumina column is based on its chemical similarities with thorium and lantanide elements reported by Abrao (2) In this case only thorium and rare earths are sorbed onto alumina from nitric acid-fluoride solutions while uranium remains in the effluent. 

Alumina, ceria, and silica particles are removed in biological wastewater treatment processes by a combination of aggregation, heteroaggregation, and sorption onto biosolids and/or extracellular polymeric substances. Some studies indicate that silica particles are less easily removed than ceria and aluminum particles. Most information on alumina, ceria, and silica removal in biological wastewater systems is from pilot- or laboratory-scale experiments, and relatively few smdies involving real CMP... 

Whereas studies have been carried out on the factors (surface coverage, residence time, pH) which influence the desorption of arsenate previously sorbed onto oxides, phyllosilicates and soils (O Reilly et al. 2001 Liu et al. 2001 Arai and Sparks 2002 Violante and Pigna 2002 Pigna et al. 2006), scant information are available on the possible desorption of arsenate coprecipitated with iron or aluminum. In natural environments arsenic may form precipitates or coprecipitates with Al, Fe, Mn and Ca. Coprecipitation of arsenic with iron and aluminum are practical and effective treatment processes for removing arsenic from drinking waters and might be as important as sorption to preformed solids. 

Lien and Zang [117] investigated the ehmination of MTBE and TAME with bifunctional aluminum. After 6 h a complete ehmination of MTBE with initial concentration of 35 mg/L was observed in the presence of oxygen. Without oxygen only 40% elimination was achieved, however, no reaction by-products were observed, indicating that the ehmination was only due to the sorption of MTBE onto the catalyst. Without bifunctional aluminum no reaction took place. The sulphuric acid treatment is decisive for the performance, since aluminum without sulfation only yielded 25% conversion of MTBE. 

An important consideration in constructing certain types of geochemical models, especially those applied to environmental problems, is to account for the sorption of ions from solution onto mineral surfaces. Metal oxides and aluminosilicate minerals, as well as other phases, can sorb electrolytes strongly because of their high reactivities and large surface areas (e.g., Davis and Kent, 1990). When a fluid comes in contact with minerals such as iron or aluminum oxides and zeolites, sorption may significantly diminish the mobility of dissolved components in solution, especially those present in minor amounts. 

Such Fe(in) and Al speciation has important implications for the geochemical evolution of AMD. At typical conditions of pH (1.5 ) and sulfate concentrations (0.01-0.1 M SO "), the mineralogy of the precipitates will be dominated by sulfates and hydroxysulfates, instead of oxides or hydroxides, as described in the next section. Further, this metal speciation can imply important differences in their sorption behavior. For example, at sulfate activities of 10 " to 10 , aluminum is present as free aqueous cation, being essentially conservative. However, at higher activities of the SO " anion (from 10 to >10 ), Al forms bisulfate anionic species (A1(S04)2) which can be sorbed onto positively charged mineral surfaces at low pH [14]. 

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