What happens when sodium reacts with zinc
Zinc is naturally present in water. The mean concentration of zinc in seawater is around 0.6-5 ppb. Zinc concentrations of 5-10 ppb are generally found in rivers. Algae contain 20-700 ppm, marine fish and mussels 3-25 ppm, oysters 100-900 ppm and crabs 7-50 ppm.
The drinking water limit value for zinc set by the World Health Organization (WHO) is 5 mg Zn2+/ L.
How and in which compounds does zinc react with water?
Elemental zinc does not react with water molecules. Together with the hydroxide ions contained in the water, the ion forms a protective, sparingly soluble layer of zinc hydroxide (Zn (OH)2). The following reaction equation applies here:
Zn2+ + 2OH- -> Zn (OH)2(s)
With the H+-Ions the following reaction takes place:
Zn (s) + 2H+ -> Zn2+(aq) + H2(G)
In this reaction, hydrogen is released, which reacts explosively with oxygen (oxyhydrogen gas effect).
Zinc salts cause a milky cloudiness in the water in higher concentrations. In addition, zinc can create an undesirable taste in the water. This happens from a concentration of about 2 mg Zn2+/ L.
Water solubility of zinc and / or its compounds
The water solubility of elemental zinc does not only depend on the temperature, but also on the pH value of the water. In the neutral range, zinc is almost insoluble, while the solubility increases rapidly at a pH value of 6 or less and also increases again from pH 11.
The element is in the dissolved state as ZnOH+(aq) or as Zn2+(aq). Also the form of the nonionic ZnCO3 (Solubility 0.21 g / L) can be found.
Examples of zinc compounds that are more or less soluble in water are: Zinc chloride (ZnCl2) with a water solubility of 4320 g / L, the water-insoluble zinc oxide (ZnO) or zinc vitriol (ZnSO4 . 7H2O) with a water solubility of 580 g / L.
Solubility and how it can be influenced
How can zinc get into the water?
The most important zinc ores are zinc blende (ZnS) and zinc spar or zinc carbonate (ZnCO3). These compounds can find their way into bodies of water through leaching from zinc ore deposits.
About three quarters of the zinc is used as metal. The rest is used as zinc compounds in various industries. The industrial wastewater from the electroplating industry, pickling plants, battery production, etc. therefore contains zinc. Zinc compounds find many other uses as well. Zinc chloride is used, among other things, for the production of parchment paper, zinc oxide in ointments and paint, as well as for catalysts, zinc vitriol as a fertilizer and zinc bacitracin as a growth-promoting agent in animal breeding. However, most of the zinc contained in wastewater and sewage sludge does not come from these point sources, but from larger surfaces.
In particular, water with a high carbonic acid content can loosen zinc from galvanized pipes and rain gutters. Zinc-containing car tires and motor oil from galvanized tanks leave zinc on the roads. In addition, zinc-containing compounds are used as fungicides or insecticides and can thus get into the water.
In the event of inadequate safety precautions, increased zinc emissions also occur in (special) landfills or landfills for building rubble.
What environmental problems can water contamination with zinc cause?
Zinc is generally not considered to be hazardous to water. However, this is elemental zinc. Zinc compounds such as zinc arsenate or zinc cyanide can even be extremely hazardous to water.
Zinc is an essential substance for humans and animals. But overdosing can have negative consequences. Above a certain concentration, zinc is even considered toxic. This toxicity is low in humans and animals. The phytotoxicity, on the other hand, should not be underestimated. Sewage sludge from wastewater treatment that is used in agriculture, forestry or horticulture should not exceed a zinc content of 3 g / kg dry matter.
In ecotoxicological tests, a PNEC value of 50 μg / L dissolved zinc was determined for zinc. This corresponds to 150-200 μg / L total zinc in the water. This PNEC value indicates the predictably ineffective concentration (Predicted No Effect Concentration).
Zinc emissions from industry have fallen sharply. Today's zinc levels therefore no longer pose a major risk to the environment. The zinc content in the Rhine, for example, is in the optimal range. Even so, there are still places with historical contamination.
Zinc naturally has five stable isotopes (e.g. 64Zn, 66Zn and 68Zn), but also fifteen unstable isotopes. 65Zn occurs, for example, in the cooling water of nuclear reactors and is used for medical diagnostic purposes.
Zinc appears to accumulate in some organisms.
What health effects can zinc cause in water?
The human body contains around 2.3 g zinc, a vital trace element. It fulfills important functions in the field of enzymes and the replication of the genetic code. The hormone insulin also contains zinc, and it plays a role in sexual maturation. The minimum intake should be 2-3 mg per day to prevent deficiency symptoms. Only about 20-40% of the zinc from food can be absorbed by the body. Mineral waters with a high zinc content are also considered healthy.
Zinc deficiency manifests itself in a lack of taste and poor appetite. In children it can also cause disorders of the immune system and the enzyme balance. A higher zinc status apparently protects against the harmful effects of cadmium. The absorption of lead in humans and animals can also be reduced by zinc. In addition, the copper / zinc ratio in the human body seems to be characteristic.
Of course, zinc can also be overdosed, but this does not happen very quickly. This can lead to acute nausea, dizziness, vomiting, colic, fever and diarrhea after ingesting about 4-8 g of zinc. Acute zinc poisoning also occurs in the form of abdominal pain and vomiting after taking 2 g of zinc sulfate.
It is also interesting that zinc, together with cadmium and mercury, is in the 12th group of the periodic table, but the other two transition metals are very toxic.
Examples of health effects of zinc compounds are:
Chemical burns of the mucous membranes from zinc chloride (lethal dose: 3-5 g) and poisoning from zinc vitriol (lethal dose: 5 g).
What water purification technologies can be used to remove zinc?
Various methods can be used to remove zinc from water. For normal applications, coagulation, ion exchangers or activated carbon are sufficient. The use of sand filters is considered very effective.
To the periodic table of the elements
To the overview of the elements and water
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