Aluminium sulphate

Endpoint summary

Additional information

Transport and distribution

 

Distribution modelling are not applicable sincealuminium sulfateis an inorganic substance whichwhen is dissolved in a large amount of neutral or slightly-alkaline water, aluminium sulfate hydrolyzes to form the aluminium hydroxide precipitate (Al(OH)3) and a dilute sulfuric acid solution and reduce the pH of soil.

 

 The rate at which soluble aluminium sulphate are gradually leached away is dependent upon the water supply. In humid regions, the upper layers of soil and rock are kept thoroughly leached, and as fast as they are formed the soluble products are removed in the drainage water. In semi-arid regions, the soils are not fully leached and soluble substances tend to accumulate.

   

The anhydrous form occurs naturally as a rare mineral millosevichite, found e.g. in volcanic environments and on burning coal-mining waste dumps. Aluminium sulfate is rarely, if ever, encountered as the anhydrous salt. It forms a number of different hydrates, of which the hexadecahydrate Al₂(SO₄)₃•16H₂O and octadecahydrate Al₂(SO₄)₃•18H₂O are the most common. The heptadecahydrate, whose formula can be written as [Al(H₂O)₆]₂(SO₄)₃•5H₂O, occurs naturally as the mineral alunogen.

 

 The above information indicates that aluminium sulphate has a propensity to leach through soil if water is applied, i.e. it does have mobility through soil, and providing sufficient water is present. As it moves downwards into layers where the water content is low, the leaching will stop.

 

On this basis, it does not have a high potential for adsorption to soil if water is not present andonly part of thealuminium sulphatein the solid phase is adsorbed.

 

On the other basis if water is present aluminium sulphate as aluminium hydroxide precipitate (Al(OH)3) have a high potential for adsorption to soil.

-          soil, the colloidal surface can adsorb large quantities ofaluminium

 

Selectivity of cation adsorption

 

The affinity of most cations for anadsorbingsurface is greater for divalent than for monovalent ions, and for large cations than for small ones of the same charge because the larger the cation the less hydrated it is. The usual affinity is:

 

Al³⁺> Ba²⁺>Sr²⁺>Ca²⁺>Mg²⁺= Cs⁺>Rb⁺>K⁺= NH₄⁺>Na⁺

 

The soil cations that are readily adsorbed onto soil colloids can be divided ino two groups. Firstly there are thebase catoins,which include the important plant nutrients Ca²⁺, Mg^{2+ ,}K⁺and Na⁺. Secondly there areacid cations,which include Al³⁺and H⁺. Related to this distinction in cations is the term base saturation, which is defined as the proportion of exchange sites occupied by base cations. A soil with a high base saturation (greater than 35%) is more fertile than a soil with a low base saturation.

Al³⁺, Ca²⁺and H⁺are the commonlyadsorbedcations in humid regions. This reflects the long-term leaching loss of basic cations and their replacement by acidic cations. In contrast, Ca^2+,Mg²⁺, K⁺and Na⁺are the commonly adsorbed cations in arid regions.

 

Aluminium influences of soil acidity

 

As clay minerals weather and break down, the aluminium in the octahedral layer is released into the soil solution, where it either reacts with water or is adsorbed onto the exchange sites of negatively charged clay minerals. Al³⁺ions are adsorbed in preference to all the other major cations. The influence that aluminium has on soil acidy is itself dependant on the acidity of the soil. At Ph less 5, aluminium is soluble and exists as Al³⁺. When Al³⁺enters the soil solution it reacts with water (it is hydrolysed) to produce H⁺ions:

 

                   Al³⁺+ H₂O <===> AlOH²⁺+ H⁺

 

Thus the acidity of the soil increases (pH falls). In soils with a pH of between 5 and 6.5, aluminium also contributes H⁺oins to the soil solution but by different mechanisms, as aluminium can no longer exist as Al³⁺ions but is converted to aluminium hydroxyl ions:

 

Al³⁺+ OH^-<===> AlOH²⁺

AlOH²⁺+H^-<===> Al(OH)₂⁺ 

                                      ^{ALUMINIUM HYDROXY IONS}

 

These hydroxyl aluminium ions act as exchangeable cations just like Al³⁺, and are adsorbed by the clay minerals. They are in equilibrium with hydroxyl aluminium ions in the soil solution, where they produce H⁺ions by the following reactions:

 

              AlOH²⁺+H₂0 <===> Al(OH)₂⁺   + H⁺

 

              Al(OH)₂⁺+H₂0 <===> Al(OH)₃⁺   + H⁺

 

In soils where the pH is above 7 Ca²⁺and Mg²⁺dominated the exchange sites and most of the hydroxyl aluminium ions have been converted to gibbsite (Al(OH)₃), is insoluble and cannot be by the negative clay minerals as no charge. In a neutral soil the exchangeable cations that dominate the cation exchange sites are the base cations, whereas in an acidics soils aluminium and hydrogen ions dominate the exchange sites.

 

On this basis if water is present aluminium sulphate as aluminium hydroxide precipitate (Al(OH)3) have a high potential for adsorption to soil.

 

The estimated Soil Adsorption Coefficient was31.82L/kg measured by calculation from EPI SuiteTM v4.0..This is Exposure Assessment Tools and Models made from EPA (Environmental Protection Agency).

Inorganic compounds are outside the estimation domain.

For Soil Adsorption Comparison Purposes:

 

Koc Estimate from MCI:

---------------------

First Order Molecular Connectivity Index ........... : 1.732

Non-Corrected Log Koc (0.5213 MCI + 0.60) .......... : 1.5027

Fragment Correction(s) --> NONE                     :  ---

Corrected Log Koc .................................. : 1.5027

 

Estimated Koc: 31.82 L/kg  <===========

 

Distribution modelling is not applicable since aluminium sulphate is an inorganic substance and it is designed for organic chemicals.

The estimated Fugacity model is applied to estimate the distribution of this substance in the environment. 

 The estimated STP Fugacity Model and Volatilization From Waterwere measured by calculation from EPI SuiteTM v4.0 Program. This is Exposure Assessment Tools and Models made from EPA (Environmental Protection Agency) .

 

 

STP Fugacity Model: Predicted Fate in a Wastewater Treatment Facility

======================================================================

(using 10000 hr Bio P,A,S)

PROPERTIES OF: Aluminium sulphate

-------------

Molecular weight (g/mol)                               346.17

Aqueous solubility (mg/l)                               1E+006

Vapour pressure (Pa)                                    1.49321E-021

               (atm)                                              1.47368E-026

               (mm Hg)                                        1.12E-023

Henry 's law constant (Atm-m3/mol)              5.10144E-030

Air-water partition coefficient                         2.08634E-028

Octanol-water partition coefficient (Kow)      1.51356E-008

Log Kow                                                       -7.82

Biomass to water partition coefficient              0.8

Temperature [deg C]                                      25

Biodeg rate constants (h^-1),half life in biomass (h) and in 2000 mg/L MLSS (h):

         -Primary tank       0.04       15.97      10000.00

         -Aeration tank      0.04       15.97      10000.00

         -Settling tank       0.04       15.97       10000.00

 

STP Overall Chemical Mass Balance:

---------------------------------

                                             g/h              mol/h         percent

 

Influent                                 1.00E+001        2.9E-002       100.00

 

Primary sludge            2.50E-002        7.2E-005        0.25

Waste sludge                         1.50E-001        4.3E-004        1.50

Primary volatilization              2.78E-027        8.0E-030        0.00

Settling volatilization               7.58E-027        2.2E-029        0.00

Aeration off gas                     1.87E-026        5.4E-029        0.00

 

Primary biodegradation          1.76E-003        5.1E-006        0.02

Settling biodegradation           5.27E-004        1.5E-006        0.01

Aeration biodegradation         6.93E-003        2.0E-005        0.07

 

Final water effluent                 9.82E+000        2.8E-002       98.15

 

Total removal                        1.85E-001        5.3E-004        1.85

Total biodegradation              9.22E-003        2.7E-005        0.09

 

 

Level III Fugacity Model (Full-Output):

=======================================

Chem Name   : Aluminium sulphate

Molecular Wt  : 346.17

Henry's LC    : 5.1e-030 atm-m3/mole (calc VP/Wsol)

Vapor Press   : 1.12e-023 mm Hg (Mpbpwin program)

Liquid VP      : 1.83e-020 mm Hg (super-cooled)

Melting Pt       : 350 deg C (Mpbpwin program)

Log Kow       : -7.82 (Kowwin program)

Soil Koc        : 86.4 (KOCWIN MCI method)

 

                      Mass Amount          Half-Life        Emissions

                        (percent)                     (hr)            (kg/hr)

Air                 2.17e-009                1.83e+003     1000

Water            18                             900                1000

Soil                81.9                          1.8e+003       1000

Sediment        0.109                        8.1e+003       0

 

                      Fugacity   Reaction      Advection   Reaction    Advection

                      (atm)         (kg/hr)         (kg/hr)     (percent)    (percent)

 

Air                 1.47e-033   3.89e-008  1.03e-006  1.3e-009   3.43e-008

Water            6.28e-035   656             852           21.9          28.4

Soil                1.34e-033   1.49e+003  0               49.7           0

Sediment        6.18e-035   0.441          0.103        0.0147       0.00344

 

Persistence Time: 1.58e+003 hr

Reaction Time:   2.2e+003 hr

Advection Time:  5.55e+003 hr

Percent Reacted: 71.6

Percent Advected: 28.4

 

Half-Lives (hr), (based upon Biowin (Ultimate) and Aopwin):

Air:                1834

Water:           900

Soil:               1800

Sediment:       8100

Biowin estimate: 2.434 (weeks-months)

 

Advection Times (hr):

Air:                100

Water:           1000

Sediment:       5e+004

 

 

Volatilization From Water

=========================

 

Chemical Name: Aluminium sulphate

 

Molecular Weight      : 346.17 g/mole

Water Solubility         : 1E+006 ppm

Vapor Pressure          : 1.12E-023 mm Hg

Henry's Law Constant: 5.1E-030 atm-m3/mole (calculated from VP/WS)

 

                                     RIVER                  LAKE

                                     ---------                ---------

Water Depth    (meters):   1                          1

Wind Velocity   (m/sec):  5                           0.5

Current Velocity (m/sec):  1                           0.05

 

HALF-LIFE (hours) :  2.135E+026       2.329E+027

HALF-LIFE (days ) :  8.897E+024       9.706E+025

HALF-LIFE (years) :  2.436E+022       2.657E+023

 

 

 

Aluminum (Al) and water

 

Aluminum and water: reaction mechanisms, environmental impact and health effects

 

The amount of aluminum in seawater varies between approximately 0.013 and 5 ppb. The Atlantic Ocean is known to contain more aluminum than the Pacific Ocean. Riverwater generallycontains about 400 ppb of aluminum.

Aluminum mainly occurs as Al3+ (aq) under acidic conditions, and as Al(OH)4- (aq) under neutral to alkalic conditions. Other forms include AlOH2+ (aq) en Al(OH)3 (aq).

Aluminum reaction with water

Aluminum metal rapidly develops a thin layer of aluminum oxide of a few millimeters that prevents the metal from reacting with water.

When this layer is corroded a reaction develops, releasing highly flammable hydrogen gas.
Aluminum chloride hydrolyses in water, and forms a mist when it comes in contact with air, because hydrochloric acid drops form when it reacts with water vapor.
Aluminum ions in other compounds also hydrolyze, and this continues until the cationic charge has run out, ending the reaction by hydroxide formation. The beginning of the hydrolysis reaction is as follows:

 

Al3+(aq) + 6H2O(l) <-> [Al(H2O)6]3+ (aq)

Solubility of aluminum and aluminum compounds

 

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 (2Al2O3 (s) + 6H+ (aq) -> Al3+ (aq) + 3H2O (l)) and in acidic form (2Al2O3 (s) + 2OH- (aq) -> AlO2- (aq) + H2O (l)).
An example of a water soluble aluminum compound is aluminum sulphate with a water solubility of 370 g/L.

Aluminum present in water

 

Aluminum forms during mineral weathering of feldspars, such as and orthoclase, anorthite, albite, micas and bauxite, and subsequently ends up in clay minerals. A number of gemstones contain aluminum, examples are ruby and sapphire.

Currently, only iron and steel are produced in larger amounts than aluminum. Additionally, aluminum is largely recycled because this is very distinctly possible. It is applied in for example frames, door knobs, car bodies, plane parts (the weight/ strength relation is very favourable), engines, cables and cans. Aluminum is a good reflector and is therefore applied in solar mirrors and heat reflecting blankets. Aluminum is processed to cans, wiring and alloys.
Aluminum salts are often added to water to start precipitation reactions for phosphate removal.

Consequently, sewage sludge in water purification with a pH value between 6.8 and 7.3 is present as hydroxides.Alums are applied as fertilizer in tea plantations. Other aluminum compounds are applied in paper production. Alloys such as duraluminum are applied because these are stronger than aluminum itself. Aluminum foam is applied in tunnels as soundproofing material.

Other examples of aluminum application include aluminum chloride use in cracking processes, aluminum oxide as an abrasive or for production of inflammable objects, aluminum sulphate use as a basic material in paper glue, tanners, mordants and synthetic rubber, and aluminum hydrogen as a reduction and hydration agent.
Aluminum occurs as an aerosol in oceanic surface layers and in waters. This is because aluminum dust end up in water. Particles end up in water through surface run-off or atmospheric transport.Generally, aluminum concentrations increase with increasing water depth

 

Environmental effects of aluminum in water

 

Aluminum may negatively affect terrestrial and aquatic life in different ways. Regular aluminum concentrations in groundwater are about 0.4 ppm, because it is present in soils as water insoluble hydroxide. At pH values below 4.5 solubility rapidly increases, causing aluminum concentrations to rise above 5 ppm. This may also occur at very high pH values.
Dissolved Al3+-ions are toxic to plants; these affect roots and decrease phosphate intake. As was mentioned above, when pH values increase aluminum dissolves. This explains the correlation between acid rains and soil aluminum concentrations. At increasing nitrate deposition the aluminum amount increases, whereas it decreases under large heather and agricultural surfaces. In forest soils it increases.

Aluminum is not a dietary requirement for plants, but it may positively influence growth in some species. It is taken up by all plants because of its wide distribution in soils. Grass species may accumulate aluminum concentrations of above 1% dry mass.

Acid rain dissolves minerals in soils, and transports these to water sources. This may cause aluminum concentrations in rivers and lakes to rise.

Aluminum naturally occurs in waters in very low concentrations. Higher concentrations derived from mining waste may negatively affect aquatic biocoenosis. Aluminum is toxic to fish in acidic, unbuffered waters starting at a concentration of 0.1 mg/L. Simultaneous electrolyte shortages influence gull permeability, and damage surface gull cells. Aluminum is mainly toxic to fish at pH values 5.0-5.5. Aluminum ions accumulate on the gulls and clog these with a slimy layer, which limits breathing. When pH values decrease, aluminum ions influence gull permeability regulation by calcium. This increases sodium losses. Calcium and aluminum are antagonistic, but adding calcium cannot limit electrolyte loss. This mainly concerns young animals. An aluminum concentration of 1.5 mg/L turned out to be fatal to trout. The element also influences growth of freshwater bony fish.
Phytoplankton contains approximately 40-400 ppm aluminum (dry mass), which leads to a bioconcentration factor of 104-105 compared to seawater.

Terrestrial organisms also contain some aluminum. Examples: mosquito larvae 7-33 ppm, springtails 36-424 ppm (dry mass). Together, pH values and aluminum concentrations determine larvae mortality.

A number of LD50 values for rats are known for aluminum. For oral intake this is 420 mg/kg for aluminum chloride, and 3671 mg/kg for aluminum nonahydrate. The mechanism of toxicity is mainly based on enzyme inhibition.

Only one non-radioactive aluminum isotope occurs naturally. There are eight instable isotopes.

Health effects of aluminum in water

The total aluminum concentration in the human body is approximately 9 ppm (dry mass). In some organs, specifically the spleen, kidneys and lung, concentrations up to 100 ppm (dry mass) may be present. Daily aluminum intake is approximately 5 mg, of which only a small fraction is absorbed. This leads to relatively low acute toxicity. Absorption is about 10 μg per day. These amounts are considered harmless to humans. Silicon may decrease aluminum uptake. However, once the element is taken up in the body it is not easily removed.
Large aluminum intake may negatively influence health. This was connected with nerve damage. Particularly people with kidney damage are susceptible to aluminum toxicity. There is a risk of allergies. Aluminum is probably mutagenic and carcinogenic. A correlation between aluminum uptake and an increased number of Alzheimer cases is suspected. However, this is uncertain because aluminum concentrations always increase with age. Increased aluminum intake may also cause osteomalacia (vitamin D and calcium deficits).
Aluminum intake mainly occurs through food and drinking water. The most recent standards were between 50 and 200 μg/L. Aluminum particles may cause functional lung disorder.
No known diseases are linked to aluminum shortages.Aluminum chloride may corrode the skin, irritate the mucous membranes in the eyes, and cause perspiration, shortness of breath and coughing. Alum increases blood clotting.

Water purification technologies applied to remove aluminum from water

 

Aluminum may be removed from water by means of ion exchange or coagulation/ flocculation. Aluminum salts are applied in water treatment for precipitation reactions. Adding aluminum sulphate and lime to water causes aluminum hydroxide formation, which leads to settling of pollutants. Hydroxide is water insoluble, therefore only 0.05 ppm dissolved aluminum remains. This is below the legal limit for drinking water of the World Health Organization (WHO), of 0.2 ppm aluminum.