Aluminium potassium bis(sulphate)

Endpoint summary

Additional information

Aluminium potassium bis (sulphate) occurs in nature as basic compounds:

Basic potassium aluminum sulfate, K[Al(OH)2]3(SO4)2 3/2 H2O, occurs in nature as loewigite. The compound is made synthetically as a rather insoluble, amorphous powder by heating aluminum sulfate, water, and an excess of potassium sulfate or by heating potassium alum with water in the ratio 1 : 4 to 200 °C. Another basic potassium aluminum sulfate, K[Al3(OH)6(SO4)2] [1302-91-6], containing less water, is the alum stone (alunite) occurring in nature.

Hydrolysis:

In aqueous solution, sediment and in humidity of soil the substance is completely dissolved and dissociated. A cluster formation, depending on concentration and time, is possible, especially near saturation point.

The trivalent aluminum ion is surrounded by six water molecules in solution. The hydrated aluminum ion, [Al(H2O)6]3+, undergoes hydrolysis, in which a stepwise deprotonation of the coordinated water ligands forms bound hydroxide ligands (e.g., [Al(H2O)5(OH)]2+, [Al(H2O)4(OH)2]+). The speciation of aluminum in water is pH dependent. The hydrated trivalent aluminum ion is the predominant form at pH levels below 4. Between pH 5 and 6, the predominant hydrolysis products are Al(OH)2+ and Al(OH)2+, while the solid Al(OH)3 is most prevalent between pH 5.2 and 8.8. The soluble species Al(OH)4- is the predominant species above pH 9, and is the only species present above pH 10. Polymeric aluminum hydroxides appear between pH 4.7 and 10.5, and increase in size until they are transformed into colloidal particles of amorphous Al(OH)3, which crystallize to gibbsite in acid waters.

In aqueous solution, potassium aluminium bis sulphate shows as other alums show all the chemical properties that their components show separately. Physical properties, such as color, electrical conductivity, and freezing-point lowering, are the sum of the properties of the components, provided the solutions are very dilute. At higher concentrations, complexes, such as [Al(SO4)2 (H2O)2], are formed. Alums are crystalline double salts of the general formula (cation 1) 1+, (cation 2)3+ and (anion2-)2 * 12 H2O. The most useful alums are those with trivalent aluminum cations and sulfate anions, (M+)(Al3+)(SO4) 2-)4*12 H2O.

Biodegradation:

Because of complete dissolution and dissociation the substance is readily biodegradable. Based on the physico-chemical properties of the substance it is to be assumed that the substance has a low absorption potential and a low partition coefficient.

Bioaccumulation potential:

In aqueous solution the substance is completely dissolved and dissociated in the cations Al3+, K+ and the anion SO42- which are dissociation products of Aluminium sulfate and Potassium sulfate which have low bioaccumulation potential (log Kow < 3). Therefore the log Kow of the substance should be very low (log Kow<3). The BCF values of aluminium of most fish are < 300 and depend on pH.

Adsorption potential:

It is to be expected from the physico-chemical properties of the substance that the absorption potential is low and the log Kow of the inorganic substance is < 3.

Transport and distribution:

With the study results of Adsorption/desorption.002 there were found indirect evidences of ionic association and cluster formation in concentrated and supersaturated solutions of KAI(SO4)2* 12H20 from the measurements of diffusion coefficients and concentration gradients in vertical columns. Strong ionic association was suspected even in the solutions of low concentration, and the sizes of the clusters increased with increasing concentration. The clusters in the supersaturated region increased much more drastically with increasing concentration and extended time. The theoretical prediction of the diffusivity and the analysis of column concentration gradients in the supersaturation range require consideration of structural details of the solution, as well as the thermodynamic solution properties.

The diffusion is one of the important main pathways for transport and distribution of chemical substances:

In general, there are four main pathways by which small molecules cross biological lipid membranes:

1. Passive diffusion. Diffusion occurs through the lipid membrane.

2. Filtration. Diffusion occurs through aqueous pores.

3. Special transport. Transport is aided by a carrier molecule, which act as a “ferryboat.”

4. Endocytosis. Transport by pinocytosis for liquids and phagocytosis for solids.

The first and third routes are important in relation to pharmacokinetic mechanisms. The aqueous pores are too small in diameter for diffusion of most drugs and toxicant, although important for movement of water and small polar molecules (e.g., urea). Pinocytosis is important for some macromolecules (e.g., insulin crossing the bloodbrain barrier).

In the publication from Kim et al. Fig. 1 shows the diffusion coefficient measured as a function of solution concentration at 25 °C.

Diffusion coefficient declined slowly but continuously with concentration in the undersaturated region and declined more rapidly in the supersaturated region.

Table 1 and 2 of the publication shows the influence of concentration and time to density, molecular weight, number of molecules

and diameter of clusters. Fig. 2 shows this influence in graphic form.

Diffusion of the heavily hydrated ionic aggregates in KAl(SO4)2*12H20 solutions can be considered as a motion of clusters.

With increasing of concentration of the substance the cluster increases and diffusion decreases.

This could be the reason why aluminium potassium bis (sulphate) is less toxic for human and environment cell membranes than aluminium sulfate because the clusters of aluminium potassium bis (sulphate) diffuse slower through the cell membranes than aluminium sulfate.