Aluminum sulphate
Silica, which is present as H4SiO4 in all natural water, may depress the solubility of aluminum by forming co-polymer layer-type minerals, such as the clay minerals. Solid basic aluminum fluoride and other mixed species may be less soluble than simple hydroxides under some conditions.  Aluminium oxide is a chemical compound of aluminium and oxygen with the chemical formula Al 2 O 3. It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium(III) oxide. Aluminium oxide is an amphoteric substance, meaning it can react with both acids and bases, such as hydrofluoric acid and sodium hydroxide, acting as an acid with a base and a base with an acid, neutralising the other and producing a salt. The most abundant aluminum compounds are aluminum oxide and aluminum hydroxide, and these are water insoluble. Aluminum oxide may be present in water both in alkalic form (2Al 2 O 3 (s) + 6H + 3+ (aq) + 3H 2 O (l)) and in acidic form (2Al 2 O 3 (s) + 2OH - 2 - (aq) + H 2 O (l)). An example of a water soluble aluminum compound is aluminum sulphate with a water solubility of 370 g/L. River water generally contains about 400 ppb of aluminum. Aluminum mainly occurs as Al 3+ (aq) under acidic conditions, and as Al(OH) 4 - (aq) under neutral to alkalic conditions. Other forms include AlOH 2 + (aq) en Al(OH) 3 (aq). Aluminium oxide is insoluble in water. In its most commonly occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools. Aluminium oxide is an amphoteric substance, meaning it can react with both acids and bases, such as hydrofluoric acid and sodium hydroxide, acting as an acid with a base and a base with an acid, neutralising the other and producing a salt. Aluminium hydroxide gels can be dehydrated (e.g. using water-miscible non-aqueous solvents like ethanol) to form an amorphous aluminium hydroxide powder, which is readily soluble in acids. All four polymorphisms have a chemical composition of aluminium trihydroxide (an aluminium atom attached to three hydroxide groups). Gibbsite is also known as hydrargillite, named after the Greek words for water (hydra) and clay (argylles). In consequence, aluminum can be found in steel as metallicaluminum and (so-called soluble aluminum), aluminum oxide and aluminumnitride. Metallic aluminum and aluminum nitride can be dissolved in acid and sothis part is called acid soluble aluminum or simply soluble aluminum. During thesteel production process, it is important to have a measure of the level of thesoluble aluminum in steel. 9 Soluble and insoluble compounds in metals with spectrolab 167Fig. 7 – Evolution of the aluminum signal from the start of the analysis. Following this discovery, the peak integration method (PIM) was introducedat SIDEX in 2000. A powder soluble in water is obtained in which the atomic ratio of bromine to aluminum is 3:2. Example 3 516 parts of crystallized aluminum iodide are dissolved in 1000 parts of water and 27 parts of alimiinum powder are added. All water-soluble salts of aluminum may be used for the new process according tothe present invention, as for example, aluminum chloride, bromide, iodide, fluoride, nitrate, acetate, formate and, for weakly basic hydroxy compounds, even the sulphate. From Wikipedia, the free encyclopedia. Aluminium hydroxide, Al(OH) 3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO(OH), and aluminium oxide (or alumina), Al 2 O 3. All four polymorphisms have a chemical composition of aluminium trihydroxide (an aluminium atom attached to three hydroxide groups). Gibbsite is also known as hydrargillite, named after the Greek words for water (hydra) and clay (argylles).
http://pubs.usgs.gov/wsp/1827b/report.pdf https://en.wikipedia.org/wiki/Aluminium_oxide http://www.lenntech.com/periodic/water/aluminium/aluminum-and-water.htm https://en.wikipedia.org/wiki/Aluminium_oxide https://en.wikipedia.org/wiki/Aluminium_hydroxide http://www.rrp.infim.ro/2006_58_2/07-Sava.pdf http://www.google.com/patents/US2196016 https://en.wikipedia.org/wiki/Aluminium_hydroxide
what type of aluminum is soluble