Aluminum leaching

FIGURE 10 Aluminum leached from glass containers by amino acids as a function of time at room temperature. Amino acid concentration 0.028 mo 1/L [53]. 

In addition to the effect of pH on mobility, the type of acid entering environmental systems may also be important. Nitric acid was found to leach more aluminum from soil columns representative of high-elevation forest floor soils than did sulfuric acid (James and Riha 1989). This is most likely due to the higher solubility of aluminum nitrate than aluminum sulfate. However, in mineral horizons below the forest floor, the study found that concentrations of aluminum leached by these acids did not differ from concentrations of aluminum leached by distilled, deionized water at a pH of 5.7. The authors concluded... 

James BR, Riha SJ. 1989. Aluminum leaching by mineral acids in forest soils I. Nitric-sulfuric acid differences. Soil Sci Soc Am J 53 259-264. 

Rajwanshi P, Singh V, Gupta MK, et al. 1997. Studies on aluminum leaching from cookware in tea and coffee and estimation of aluminum content in toothpaste, baking powder and paan masala. Sci Total Environ 193 243-249. 

Tennakone BK, Wickramanayake S. 1987. Aluminum leaching from cooking utensils. Nature 325 202. 

Cronan C. S. and Schofield C. L. (1979) Aluminum leaching response to acidic precipitation effects on high-elevation watersheds in the Northeast US. Science 204, 304-306. 

Homogeneous coatings of zeolite ZSM-5 were prepared by the seed film method on porous ceramic foams and on alumina spheres. The zeolite was predominately present in the form of a film on the support surface rather than as aggregated crystals on the surface. The results from gas adsorption and SEM analysis indicated that the entire surface of the foams was successfully covered with a 450 nm film. A 500 nm film was formed on the external surface and also in pores close to the external surface of the spheres. Zeolite was not formed on the internal surface of the alumina spheres. Aluminum leaching from the foams was observed but did not seem to have any detrimental effects on the substrates. 

Cronan, C.S. and C.L. Schofield, 1979. Aluminum Leaching Response to Acid Precipitation Effects on High Elevation Watersheds in the Northeast Science 204, pp. 304-305. 

Fondeur, F.F., Hobbs, D.T., and Fink, S.D. (2004) Aluminum Leaching of Archived Sludge from Tanks 8F, IIH and 12 H. WSRC-TR-2004-00180, Westinghouse Savanna River Company, Aiken, SC 29808, USA. 

Aluminum—It is not certain whether it is safe to cook such highly acid foods as rhubarb and tomatoes in aluminum pots and pans, because aluminum is dissolved by acid solutions. Abnormally large intakes of aluminum have irritated the digestive tract. Also, unusual conditions have sometimes permitted the absorption of sufficient aluminum from antacids to cause brain damage. Even if the amounts of aluminum leached from aluminum utensils by acid foods are not toxic, there is the possibility that insoluble complexes might be formed between the aluminum and some of the trace minerals, so that the absorption of these nutrients is blocked. 

In 1990, appioximately 66,000 metric tons of alumina trihydiate [12252-70-9] AI2O2 3H20, the most widely used flame retardant, was used to inhibit the flammabihty of plastics processed at low temperatures. Alumina trihydrate is manufactured from either bauxite ore or recovered aluminum by either the Bayer or sinter processes (25). In the Bayer process, the bauxite ore is digested in a caustic solution, then filtered to remove siUcate, titanate, and iron impurities. The alumina trihydrate is recovered from the filtered solution by precipitation. In the sinter process the aluminum is leached from the ore using a solution of soda and lime from which pure alumina trihydrate is recovered (see Aluminum compounds). 

Sodium aluminate [1302-42-7] is another source of soluble aluminum made by leaching bauxite with caustic soda. As with alum, the active species are really its hydrolysis products which depend on the chemistry of the system to which it is added. It tends to raise the pH. It is available both as a soHd and as a solution (see Aluminum compounds, aluminates). 

Solid Superacids. Most large-scale petrochemical and chemical industrial processes ate preferably done, whenever possible, over soHd catalysts. SoHd acid systems have been developed with considerably higher acidity than those of acidic oxides. Graphite-intercalated AlCl is an effective sohd Friedel-Crafts catalyst but loses catalytic activity because of partial hydrolysis and leaching of the Lewis acid halide from the graphite. Aluminum chloride can also be complexed to sulfonate polystyrene resins but again the stabiUty of the catalyst is limited. 

A commercial process which uses hydrothermal leaching on a large scale is the Bayer process for production of aluminum oxide (see Aluminum compounds). This process is used to extract and precipitate high grade alurninum hydroxide (gibbsite [14762-49-3]) from bauxite [1318-16-7] ore. The hydrothermal process step is the extraction step in which concentrated sodium hydroxide is used to form a soluble sodium aluminate complex ... 

Other recovery methods have been used (10). These include leaching ores and concentrates using sodium sulfide [1313-82-2] and sodium hydroxide [1310-73-2] and subsequentiy precipitating with aluminum [7429-90-3], or by electrolysis (11). In another process, the mercury in the ore is dissolved by a sodium hypochlorite [7681-52-9] solution, the mercury-laden solution is then passed through activated carbon [7440-44-0] to absorb the mercury, and the activated carbon heated to produce mercury metal. Mercury can be extracted from cinnabar by electrooxidation (12,13). 

A.lkaline Solutions. The most important example of alkaline leach is the digestion of hydrated alumina from bauxite by a sodium hydroxide solution at 160-170°C, ie, the Bayer process (see Aluminumand aluminum alloys). 

Aluminum. All primary aluminum as of 1995 is produced by molten salt electrolysis, which requires a feed of high purity alumina to the reduction cell. The Bayer process is a chemical purification of the bauxite ore by selective leaching of aluminum according to equation 35. Other oxide constituents of the ore, namely siUca, iron oxide, and titanium oxide remain in the residue, known as red mud. No solution purification is required and pure aluminum hydroxide is obtained by precipitation after reversing reaction 35 through a change in temperature or hydroxide concentration the precipitate is calcined to yield pure alumina. 

Potassium alum is manufactured by treating bauxite with sulfuric acid and then potassium sulfate. Alternatively, aluminum sulfate is reacted with potassium sulfate, or the mineral alum stone, alunite, can be calciaed and leached with sulfuric acid. Alunite is a basic potassium aluminum sulfate... 

A beryUium concentrate is produced from the leach solution by the counter-current solvent extraction process (10). Kerosene [8008-20-6] containing di(2-ethylhexyl)phosphate [298-07-7] is the water-immiscible beryUium extractant. The slow extraction of beryUium at room temperature is accelerated by warming. The raffinate from the solvent extraction contains most of the aluminum and aU of the magnesium contained in the leach solution. 

The loaded organic phase is stripped of beryUium using an aqueous ammonium carbonate [506-87-6] solution, apparently as a highly soluble ammonium beryUium carbonate [65997-36-6] complex, (NH 4Be(C02)3. AU of the iron [7439-89-6] contained in the leach solution is coextracted with the beryUium. Heating the strip solution to about 70°C separates the iron and a smaU amount of coextracted aluminum as hydroxide or basic carbonate... 

Hydrochloric acid digestion takes place at elevated temperatures and produces a solution of the mixed chlorides of cesium, aluminum, and other alkah metals separated from the sUiceous residue by filtration. The impure cesium chloride can be purified as cesium chloride double salts such as cesium antimony chloride [14590-08-0] 4CsCl SbCl, cesium iodine chloride [15605 2-2], CS2CI2I, or cesium hexachlorocerate [19153 4-7] Cs2[CeClg] (26). Such salts are recrystaUized and the purified double salts decomposed to cesium chloride by hydrolysis, or precipitated with hydrogen sulfide. Alternatively, solvent extraction of cesium chloride direct from the hydrochloric acid leach Hquor can be used. 

Modem manufacturing processes quench the roast by continuous discharge into the leach water held in tanks equipped with agitators. At this point the pH of the leach solution is adjusted to between 8 and 9 to precipitate aluminum and siHcon. The modem leaching operations are very rapid because no or htde lime is used. After separation of the ore residue and precipitated impurities using rotary vacuum filters, the cmde Hquid sodium chromate may need to be treated to remove vanadium, if present, in a separate operation. The ore residue and precipitants are either recycled or treated to reduce hexavalent chromium to Cr(III) before disposal. 

Sulfide Ores ores. In the Zairian ores, cobalt sulfide as carroUite is mixed with chalcopyrite and chalcocite [21112-20-9]. For processing, the ore is finely ground and the sulfides are separated by flotation (qv) using frothers. The resulting products are leached with dilute sulfuric acid to give a copper—cobalt concentrate that is then used as a charge in an electrolytic cell to remove the copper. Because the electrolyte becomes enriched with cobalt, solution from the copper circuit is added to maintain a desirable copper concentration level. After several more steps to remove copper, iron, and aluminum, the solution is treated with milk of lime to precipitate the cobalt as the hydroxide. 

Consider a lake with a smaU watershed in a forest ecosystem. The forest and vegetation can be considered as an acid concentrator. SO2, NO2, and acid aerosol are deposited on vegetation surfaces during dry periods and rainfalls they are washed to the soil floor by low-pH rainwater. Much of the acidity is neutralized by dissolving and mobilizing minerals in the soil. Aluminum, calcium, magnesium, sodium, and potassium are leached from the soil into surface waters. The ability of soils to tolerate acidic deposition is very dependent on the alkalinity of the soil. The soil structure in the... 

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