Reaction mass of aluminium chloride, iron dichloride, magnesium chloride and manganese dichloride

Endpoint summary

Additional information

Iron

For inorganic substances present in the natural environment, discussion is necessarily qualitative and modeling processes cannot be used easily. For a ubiquitous substance, the measured environmental concentrations (see discussion of environmental fate and pathways) constitute sufficient information about ultimate environmental fate and behaviour. Under normal aerobic environmental conditions, anthropogenic iron salt emissions will primarily mineralise with water, precipitate as ferric hydroxide and be incorporated into soil and sediment, and participate in the natural geochemical processes of iron. Under anaerobic conditions or low pH other processes will dominate the environmental fate of iron.

Soil is the primary reservoir of naturally occurring iron. It has its own surface geochemical cycle. Iron can be mobilized from soil or sediment to surface waters as colloidal ferric hydroxide, fine suspended particulates and inbound to clay silt. Factors like pH, CO2 concentration, redox conditions, availability of organic and inorganic complexing agents and soil type contribute to reactions of iron in soil. In soil iron can be bound to organic humic substances (see below), which can be soluble, colloidal or precipitates depending on the environmental factors (Lahermo et al 1996).

Mass balances and precipitation of iron were studied in two acidified (pH < 5) Czech lakes in 2000 - 2003, where influent iron was mainly in the organically bound form. Photochemical reactions were observed to liberate iron to the inorganic form, subject to precipitation of iron hydroxides. These hydroxides were concluded to decrease the availability of orthophosphate to phytoplankton, and to increase the amount of iron hydroxides in lake sediment, changing its phosphate sorption characteristics (Kopacek et al 2005).

Sediments contain Fe(III) as insoluble oxides, but also in an organically complexed and colloidal state. Even though 60 – 80% of iron is bound to silicates in marine sediments, Fe(III) hydroxides are considered to be the main species linked to binding and cycling of phosphorus in surface waters. They can act as chemical coagulants of external phosphorus loading but also as internal source of phosphorus under strong reducing conditions, caused e.g. by sedimented organic matter. Basic environmental factors are as availability of oxygen, pH, sulphate, microbiological reduction and sedimented organic matter. Dynamics of phosphorus has been studied in brackish marine sediments (Gulf of Finland) in detail (Lehtoranta 2003).

• Lehtoranta J (2003). Dynamics of sediment phosphorus in the brackish Gulf of Finland. Monographs of the Boreal Environmental Research 24, 2003. Finnish Environmental Institute, Helsinki, Finland. 58 pp. 6 - 15
• Lahermo P, et al (1996). Geochemical Atlas of Finland. Part 3: Environmental Geochemistry – stream waters and sediments. 5.12. Rauta (Fe). Pp. 79 – 81, 113
• Kopacek J, Klementova S, Norton SA (2005): Photochemical Production of Ionic and Particulate Aluminum and Iron in Lakes. Environ. Sci. Technol. 2005, 39(10), 3656-3662Kopacek et al 2005

Manganese

Removal of iron and manganese from solution via precipitation and abiotic processes is dominant. A complex series of oxidation/precipitation and adsorption reactions occurs when Mn(II) is present in aerobic environments, which eventually renders the manganese biologically unavailable as insoluble manganese dioxide (CICAD Concise International Chemical Assessment Document 63, WHO 2004 and 2005).

• WHO World Health Organization (2004 and 2005). Manganese and its Compounds: Environmental Aspects. Concise International Chemical Assessment Document 63, Corrigenda published by 12 April 2005 have been incorporated. Self-published, Geneva, Switzerland

Aluminium

Aluminium is the most abundant metal in the earth’s crust, but is never found in its elemental state in nature. In compounds, aluminium occurs in its only oxidation state (+3) (Lide 2005). Aluminum occurs widely in nature with silicates, such as mica and feldspar, as the hydroxo oxide (bauxite), and as cryolite (Na3AlF6) (Cotton et al 1999). The transport and partitioning of aluminium in the environment is determined by its chemical properties, as well as the characteristics of the environmental matrix that affect its solubility.

In groundwater or surface water systems, an equilibrium with a solid phase form is established that largely controls the extent of aluminium dissolution which can occur. In addition to the effect of pH on mobility, the type of acid entering environmental systems may also be important (ATSDR 2008). The ability of mineralized soil to control the migration of aluminium was observed in another study. Acidic leachate from coal waste containing aluminium was percolated through soil containing varying amounts of calcium carbonate (Wangen & Jones 1984). Soluble aluminium was found to decrease dramatically as the pH of the percolating leachate increased and aluminium oxide precipitates formed; at pH 6, no dissolved aluminium was measured. The authors concluded that alkalinized carbonaceous soils provide the best control material for acidic leachates from coal mineral wastes.

The adsorption of aluminium onto clay surfaces can be a significant factor in controlling aluminium mobility in the environment, and these adsorption reactions, measured in one study at pH 3.0–4.1, have been observed to be very rapid (Walker et al. 1988). However, clays may act either as a sink or a source for soluble aluminium depending on the degree of aluminium saturation on the clay surface (Walker et al 1988).

Aluminum, as a constituent of soil, weathered rock, and solid waste from industrial processes, is transported through the atmosphere as windblown particulate matter and is deposited onto land and water by wet and dry deposition (ATSDR 2008).

• ATSDR Agency for Toxic Substances and Disease Registry (2008). Toxicological Profile for Aluminum. U.S. Department of Health and Human Services, Public Health Service, Atlanta, Georgia, U.S.A. 357 p
• Cotton FA, Wilkinson G, Murillo CA, et al (Eds) (1999). The group 13 elements: Al, Ga, In, Tl. Advanced inorganic chemistry. 6th ed. New York, NY: John Wiley & Sons, Inc., 175-207.
• Walker WJ, Cronan CS, Patterson HH (1988). A kinetic-study of aluminum adsorption by aluminosilicate clay-minerals. Geochim Cosmochim Acta 52:55-62.
• Wangen LE, Jones MM (1984). The attenuation of chemical elements in acidic leachates from coal mineral wastes by soils. Environ Geol Water Sci 6:161-170.