Aluminium sulphate

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Additional information

Aluminum sulfate is stable and having a high melting point of 770 deg °C .Aluminim sulphate is stable in air, sunlight and to metals.

Solid product is stable for long periods if kept dry and at ambient temperatures. Legal shelf-life of aluminim sulphate is 60 months.

 

Aluminum sulfate cannot be oxidized and atmospheric transformations would not be expected to occur during transport. If aluminum metal particulates were released to air during metal processing, they would be rapidly oxidized. It is not applicable for an inorganic compound wich dissociates

 

Aluminum sulfate is an inorganic substance with a relatively large number of oxygen atoms per molecule but no hydrogen or carbon atoms. There are no structural alerts with regard to oxidising potential of the substance.

 

In air, hydrated aluminum sulfate will react with moisture and produce sulfuric acids, and aluminum oxide. Since these aluminum sulfate is usually not emitted to air, the amount of aluminum present in air would be negligible compared with the amount coming from natural erosion of soil.

REFERENCES:

TOXICOLOGICAL PROFILE FOR ALUMINUM, U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES, Public Health ServiceAgency for Toxic Substances and Disease Registry, p.191, 2008.

Canadian Environmental Protection Act, 1999, PRIORITY SUBSTANCES LIST ASSESSMENT REPORT of Aluminium chloride, nitrate and sulphate, Environment Canada Health Canada, p. 17, 2008

 

Hydrolysis is a chemical reaction during which molecules of water (H2O) are split into hydrogen cations (H+, conventionally referred to as protons) and hydroxide anions (OH−) in the process of a chemical mechanism).

 

When released into water, the aluminum sulphate hydrolyses to form aluminum hydroxides.

Reactions between aluminum sulphate, water and associated “impurities” result in the formation of a floc, which separates from the water phase to form alum sludge. A small fraction of the aluminum can stay in the water in either colloidal or dissolved form.The different reactions involved in the formation of aluminum hydroxide in aqueous solutionwasdescribed; the overall reaction can be represented by the following equation:

Al2(SO4)3+ 6H2O<=>2Al(OH)3⁰+ 3H2SO4

The aluminum hydroxide present in sludge is expected to remain mostly solid following release into surface water.Experiments wereshowed that less than 0.2% of the aluminum hydroxide present in sludge was released in supernatant water at a pH of 6 and less than 0.0013% was released at pH 7.65. In both cases, aluminum hydroxide was present mostly in particulate form. At these pH values, aluminum solubility is low and kinetics favour the formation of solid aluminum hydroxide.

 

When used to treat sewage water, alum will also react with phosphate, as shown in the following reaction:

Al2(SO4)3+ 2PO4^3– <=> AlPO4(s) + 3SO4^2–

 

This process has been used for many years to treat phosphorus in wastewaters, as well as to reduce phosphorus levels in runoff from land fertilized with poultry litter and restore phosphorus-enriched eutrophic lakes .

Aluminum is a strongly hydrolysing metal and is relatively insoluble in the neutral pH range (6.0–8.0) . In the presence of complexing ligands and under acidic (pH < 6) and alkaline (pH > 8) conditions, aluminum solubility is enhanced. At low pH values, dissolved aluminum is present mainly in the aquo form (Al3+).

 

Hydrolysis occurs as pH rises, resulting in a series of less soluble hydroxide complexes (e.g., Al(OH)2+, Al(OH)2+). Aluminum solubility is at a minimum near pH 6.5 at 20°C and then increases as the anion, Al(OH)4–, begins to form at higher pH.

 

Temperature has been shown to influence the solubility, hydrolysis and molecular weight distribution of aqueous aluminum species as well as the pH of solutions.There wasreported a higher degree of aluminum hydrolysis and greater polymerization to high molecular weight species in inorganic aluminum solutions stored for one month at 25°C compared with those stored for an equivalent period at 2°C. The researchers hypothesized that more advanced polymerization evident at the higher temperature resulted in more deprotonation and condensation reactions, possibly accounting for the observed lower pH of the 25°C test solutions (range 4.83 to 5.07 versus 5.64 to 5.78 in the solutions at 2°C).

 

 

In water, Aluminum sulphate is likely to disappear rapidly, because of its high water solubility and non- volatility; 

 

Chemical decomposition or phototransformation induced by light or other radiant energy is not possible because Aluminium sulphate as an inorganic compound cannot broken down by photons.