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The influence of the complexation of humic substances on the migration forms of metals in natural waters, areas of northern taiga and forest-steppe of the Tyumen region

Name
Marina
Surname
Dinu
Scientific organization
Tyumen State University (Laboratory of Water Quality) Grant № 11G34.31.0036 (2010-2012 gg.). Institute 0f geochemistry and analytical chemistry by Vernadsky
Academic degree
PhD of Chemistry
Position
Senior Researcher
Scientific discipline
Earth Sciences, Ecology & Environmental Management
Topic
The influence of the complexation of humic substances on the migration forms of metals in natural waters, areas of northern taiga and forest-steppe of the Tyumen region
Abstract
Work is devoted assessing the impact of complexation of metal ions with humic substances of natural waters on the distribution of metals into molds. Applied to published data on the values of the conditional stability constants of complexes to describe theactivity of the metal in the environment. The different approaches to the estimation of complexing ability of metal ions in natural waters, the degree of toxicity and migratory activity. The features of the chemical composition of water and foreststeppe zones of the northern taiga.
Keywords
humus, water, complex, toxic
Summary

Natural water as a complex multicomponent heterophase polydisperse systems are characterized by various forms of metal. Component interaction processes in the waters are manifold: hydrolysis, polymerization, formation of colloids and suspensions, complex. These and many other reactions cause one of the main features of the composition of natural waters is the presence in the solution of a number of coexisting chemical forms for each component [1-8].

The chemical forms of the elements differ in the migration capacity, reactivity, stability in natural waters.

If you change the physical and chemical conditions occur metal moving from one phase to another [1-4], [6-18]. [1-4], [6-18]. Depending on the environmental conditions (pH, redox potential, amount of ligand and other factors) metals exist in different oxidation states and are included in different compounds. Furthermore, all metals in the aqueous phase tend to an equilibrium state in which the forms coexist according to their physicochemical characteristics.

Study of the processes of complexation of metals with humic substances (HS) allows to predict the proportion of dissolved and colloidal forms of metals and the level of water toxicity. Dissolved form is characteristic of metals in the environment only in unpolluted waters c low turbidity (suspended solids content of at least 5-10 mg / l) [1-4], [9]. Low pH and Eh, small amounts of of suspended matter, high HS [1-4], [10-18] promote dissolution of metals, their existence in ionic form. Ionic forms of [6-8] is the most reactive and mobile, have the greatest toxicity. Therefore, abnormally acidic water in addition to the direct negative impact is transported in large amounts, many metal ions. Cations Cr (III), for example, can be carried only in very acidic environments and are deposited at an elevated alkalinity [5], [12-18]. You can say that the acidic and weakly acidic solutions c pH <6 are favorable for the transfer of the majority of trace elements in the form of ions. Increasing the pH of the medium mainly contributes to lower mobility due to deposition, as mentioned above. Complexes of metals with HS depending on the molecular weight are dissolved and colloidal form, as indicated above, each of which is characterized by a certain degree of stability. Changing the stability of metal complexes with HS determined, firstly, the physicochemical characteristics of metal, and secondly, the qualitative composition of the organic components [12-13], third, molecular weight HS [1-4], [9].

One of the important processes that determine the migration ability of trace elements in surface waters, is the interaction of metal ions with HS treatment, which has a significant impact, both on the mobility and distribution of metal into molds.

The aim of the work was carried out theoretical calculations of finding forms of metals in natural waters of forest-steppe zone and northern taiga by the results of detailed studies of natural water chemical composition on the territory of the Tyumen region. During operation the following parameters were used: the content of metal ions, the amount of water of organic matter, pH, content of inorganic anions. In the calculation takes into account the flow of competitive reactions, material balance and electroneutrality of the system. Data on conditional constants of metal complexes with humic substances were used in [18], taking into account the specifics of humic substances.

Results and its discussion. Each natural water body is an individual chemical system in which multiple factors influence the form of metal finding. The presence in the systems of inorganic anions and cations effect on the complexation process with HS, through the course of competing reactions. Analysis of the published data, and we have obtained experimental and calculated results showed the influence of the functional characteristics of different soil humic substances in the form of metal finding.

Natural waters of the northern boreal forest are characterized by lower levels of pH and total alkalinity than water-steppe zone, which affects the distribution of metals prone to hydrolysis. These include aluminum, copper, nickel. Also this fact affects the formation of the carbonate complexes of alkaline earth metal ions. If the natural waters of the forest-steppe zone of much of the alkaline earth metal is connected to the carbonate complexes, the waters of the northern boreal forest are more common form of metal ion is located. According to our data, strontium, as the representative alkaline earth metal ion is in the form of natural waters in these zones. Low concentrations of alkaline earth metals in natural waters zone northern boreal forest (Table. 2) in the presence of high (> 100 mg / l) of aluminum and iron concentrations contribute to the low binding of calcium and magnesium ions with humic treatment substances, especially if they contain organic compounds of less than 10 mg O / l.

The ions Fe (III) and Al (III) are found in high amounts (more than 100 g / L), and natural waters of northern boreal forest and steppe natural waters zone. It is worth noting the high degree of binding iron ions with humic substances in all of the investigated object. Al (III) ion is less studied, that does not allow you to compare the results obtained with the works of other authors. It is known that Al (III) ions are able to form complexes with HS par with ions Fe (III) [6-8], but due to the diverse chemical composition of water bodies with the degree of binding of HS can vary greatly.

For example, in natural waters grove belt zone differences between the aqua ions and complex forms of Al (III) constitute more than 50-70%. Low concentrations of ions of copper, zinc and lead (less than 2 mg / L) in natural water areas forest-steppes on the rule of Le Chatelier cause predominantly aqua ions type of migration of metals, but in natural objects zone of northern taiga the degree of binding of copper ions with humic substances waters reach 20%. Cadmium in natural water areas of northern taiga and steppe is in the ionic form, which is facilitated by the low conditional constants ustoychivostikompleksov [18] and low levels of cadmium in natural waters. The complexation of nickel ions in individual water bodies of the steppe zone and northern boreal forest at low competitive environment and quantities of humus more than 10 mg O / l up to 70%, due to the low competitiveness of the humic substances in the given object. Mn (II) in natural waters Tyumensky region is in ionic form, due to low stability constants of metal complexes, and small concentrations.

Cr (III) in natural materials is advantageously in the form of hydroxil and practically does not form compounds of humic substances with water. Analyzing the form of metal finding, we may conclude that a large variability in the forms of distribution of metals in natural waters, which are determined by the composition and concentration of trace elements, especially humic substances. The chemical properties of HS in natural waters depends, in turn, on soil properties, located in the catchment area and therefore have a zonal specificity. Based on the distribution of metals in forms hazardous properties of such metals as aluminum, iron, copper occur in natural waters with low humus high total alkalinity. The toxic properties of cadmium, lead, nickel, zinc occur in the presence of large amounts of iron ions, copper, aluminum, i.e. in the presence of strong competitor’s system complexation with humic substances.

There are complex mechanisms for binding and distributing forms of metals in natural waters, which are determined not only by the properties of metal ions as the overall chemistry of the water, including the entire range of metal content, as well as individual quality characteristics of humic substances. Each water system has a unique set of chemical components and HS. Physical and chemical properties of metal ions, their content, as well as the concentration of cations and anions caused specific trends in metal migration.

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