Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
11 décembre 2011 7 11 /12 /décembre /2011 03:46

Dietary intake

In the U.S., the Recommended Dietary Allowance (RDA) is 8 mg/day for women and 11 mg/day for men.HP Pavilion DV4-1281US Battery

 Median intake in the U.S. around 2000 was 9 mg/day for women and 14 mg/day in men.[169] Oysters, lobster [170] and red meats, especially beef, lamb and liver have some of the highest concentrations of zinc in food.[152]

The concentration of zinc in plants varies based on levels of the element in soil.HP Pavilion DV4-1282CM Battery

When there is adequate zinc in the soil, the food plants that contain the most zinc are wheat (germ and bran) and various seeds (sesame, poppy, alfalfa, celery, mustard).[171] Zinc is also found in beans, nuts, almonds, whole grains, pumpkin seeds, sunflower seeds and blackcurrant.HP Pavilion DV4-1283CL Battery

Other sources include fortified food and dietary supplements, which come in various forms. A 1998 review concluded that zinc oxide, one of the most common supplements in the United States, and zinc carbonate are nearly insoluble and poorly absorbed in the body.HP Pavilion DV4-1287CL Battery

 This review cited studies which found low plasma zinc concentrations after zinc oxide and zinc carbonate were consumed compared with those seen after consumption of zinc acetate and sulfate salts. However, harmful excessive supplementation is a problem among the relatively affluent,HP Pavilion DV4-1290BR Battery

and should probably not exceed 20 mg/day in healthy people,[174] although the U.S. National Research Council set a Tolerable Upper Intake of 40 mg/day.

For fortification, however, a 2003 review recommended zinc oxide in cereals as cheap, stable, and as easily absorbed as more expensive forms.HP Pavilion DV4-1290EL Battery

 A 2005 study found that various compounds of zinc, including oxide and sulfate, did not show statistically significant differences in absorption when added as fortificants to maize tortillas. A 1987 study found that zinc picolinate was better absorbed than zinc gluconate or zinc citrate.HP Pavilion DV4-1292CM Battery

However, a study published in 2008 determined that zinc glycinate is the best absorbed of the four dietary supplement types available. 

 Deficiency

Zinc deficiency is usually due to insufficient dietary intake, but can be associated with malabsorption,HP Pavilion DV4-1299EE Battery

acrodermatitis enteropathica, chronic liver disease, chronic renal disease, sickle cell disease, diabetes, malignancy, and other chronic illnesses. Symptoms of mild zinc deficiency are diverse. Clinical outcomes include depressed growth, diarrhea, impotence and delayed sexual maturation,HP Pavilion DV4-1300 CTO Battery

alopecia, eye and skin lesions, impaired appetite, altered cognition, impaired host defense properties, defects in carbohydrate utilization, and reproductive teratogenesis.[163] Mild zinc deficiency depresses immunity,[180] although excessive zinc does also.HP Pavilion DV4-1301TU Battery

Animals with a diet deficient in zinc require twice as much food in order to attain the same weight gain as animals given sufficient zinc.[115]

Groups at risk for zinc deficiency include the elderly, and those with renal insufficiency. The zinc chelator phytate, found in seeds and cereal bran, can contribute to zinc malabsorption.HP Pavilion DV4-1301TX Battery

Despite some concerns,[181] western vegetarians and vegans have not been found to suffer from overt zinc deficiencies any more than meat-eaters.[182] Major plant sources of zinc include cooked dried beans, sea vegetables, fortified cereals, soyfoods, nuts, peas, and seeds.HP Pavilion DV4-1302TU Battery

However, phytates in many whole-grains and fiber in many foods may interfere with zinc absorption and marginal zinc intake has poorly understood effects. There is some evidence to suggest that more than the US RDA (15 mg) of zinc daily may be needed in those whose diet is high in phytates, such as some vegetarians.HP Pavilion DV4-1302TX Battery

These considerations must be balanced against the fact that there is a paucity of adequate zinc biomarkers, and the most widely used indicator, plasma zinc, has poor sensitivity and specificity.[183] Diagnosing zinc deficiency is a persistent challenge.[1]

Nearly two billion people in the developing world are deficient in zinc.HP Pavilion DV4-1303TU Battery

In children it causes an increase in infection and diarrhea, contributing to the death of about 800,000 children worldwide per year.[1] The World Health Organization advocates zinc supplementation for severe malnutrition and diarrhea.HP Pavilion DV4-1303TX Battery

Zinc supplements help prevent disease and reduce mortality, especially among children with low birth weight or stunted growth.[184] However, zinc supplements should not be administered alone, since many in the developing world have several deficiencies, and zinc interacts with other micronutrients.HP Pavilion DV4-1304TU Battery

Zinc deficiency is crop plants' most common micronutrient deficiency; it is particularly common in high-pH soils. Zinc-deficient soil is cultivated in the cropland of about half of Turkey and India, a third of China, and most of Western Australia, and substantial responses to zinc fertilization have been reported in these areas.HP Pavilion DV4-1304TX Battery

Plants that grow in soils that are zinc-deficient are more susceptible to disease. Zinc is primarily added to the soil through the weathering of rocks, but humans have added zinc through fossil fuel combustion, mine waste, phosphate fertilizers, limestone, manure, sewage sludge, and particles from galvanized surfaces.HP Pavilion DV4-1305TU Battery

 Excess zinc is toxic to plants, although zinc toxicity is far less widespread.

Toxicity

Although zinc is an essential requirement for good health, excess zinc can be harmful. Excessive absorption of zinc suppresses copper and iron absorption.HP Pavilion DV4-1305TX Battery

The free zinc ion in solution is highly toxic to plants, invertebrates, and even vertebrate fish.[186] The Free Ion Activity Model is well-established in the literature, and shows that just micromolar amounts of the free ion kills some organisms. A recent example showed 6 micromolar killing 93% of all Daphnia in water.HP Pavilion DV4-1306TU Battery

The free zinc ion is a powerful Lewis acid up to the point of being corrosive. Stomach acid contains hydrochloric acid, in which metallic zinc dissolves readily to give corrosive zinc chloride. Swallowing a post-1982 American one cent piece (97.5% zinc) can cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach.HP Pavilion DV4-1306TX Battery

There is evidence of induced copper deficiency at low intakes of 100–300 mg Zn/day; a recent trial had higher hospitalizations for urinary complications compared to placebo among elderly men taking 80 mg/day.[189] The USDA RDA is 11 and 8 mg Zn/day for men and women, respectively.HP Pavilion DV4-1307TU Battery

Even lower levels, closer to the RDA, may interfere with the utilization of copper and iron or adversely affect cholesterol.[167]Levels of zinc in excess of 500 ppm in soil interfere with the ability of plants to absorb other essential metals, such as iron and manganese.HP Pavilion DV4-1307TX Battery

There is also a condition called the zinc shakes or "zinc chills" that can be induced by the inhalation of freshly formed zinc oxide formed during the welding of galvanized materials. 

The U.S. Food and Drug Administration (FDA) has stated that zinc damages nerve receptors in the nose, which can cause anosmia.HP Pavilion DV4-1308TU Battery

 Reports of anosmia were also observed in the 1930s when zinc preparations were used in a failed attempt to prevent polio infections. On June 16, 2009, the FDA said that consumers should stop using zinc-based intranasal cold products and ordered their removal from store shelves.HP Pavilion DV4-1308TX Battery

 The FDA said the loss of smell can be life-threatening because people with impaired smell cannot detect leaking gas or smoke and cannot tell if food has spoiled before they eat it. Recent research suggests that the topical antimicrobial zinc pyrithione is a potent heat shock response inducer that may impair genomic integrity with induction of PARP-dependent energy crisis in cultured human keratinocytesand melanocytes.HP Pavilion DV4-1309TU Battery

Poisoning

In 1982, the United States Mint began minting pennies coated in copper but made primarily of zinc. With the new zinc pennies, there is the potential for zinc toxicosis, which can be fatal.HP Pavilion DV4-1309TX Battery

One reported case of chronic ingestion of 425 pennies (over 1 kg of zinc) resulted in death due to gastrointestinal bacterial and fungal sepsis, while another patient, who ingested 12 grams of zinc, only showed lethargy and ataxia (gross lack of coordination of muscle movements).HP Pavilion DV4-1310TU Battery

Several other cases have been reported of humans suffering zinc intoxication by the ingestion of zinc coins. 

Pennies and other small coins are sometimes ingested by dogs, resulting in the need for medical treatment to remove the foreign body.HP Pavilion DV4-1310TX Battery

The zinc content of some coins can cause zinc toxicity, which is commonly fatal in dogs, where it causes a severe hemolytic anemia, and also liver or kidney damage; vomiting and diarrhea are possible symptoms.[196] Zinc is highly toxic in parrots and poisoning can often be fatal.HP Pavilion DV4-1311TU Battery

 The consumption of fruit juices stored in galvanized cans has resulted in mass parrot poisonings with zinc.

Zinc smelting is the process of converting zinc concentrates (ores that contain zinc) into pure zinc.HP Pavilion DV4-1311TX Battery

The most common zinc concentrate processed is zinc sulfide,[1] which is obtained by concentratingsphalerite using the froth flotation method. Secondary (recycled) zinc material, such as zinc oxide, is also processed with the zinc sulfide.[2] Approximately 30% of all zinc produced is from recycled sources.HP Pavilion DV4-1312TU Battery

There are two methods of smelting zinc: the pyrometallurgical process and the electrolysis process.[2]Both methods are still used.[2][4] Both of these processes share the same first step: roasting.

Roasting is a process of oxidizing zinc sulfide concentrates at high temperatures into an impure zinc oxide, called "Zinc Calcine". The chemical reactions taking place during the process are:HP Pavilion DV4-1312TX Battery

Approximately 90% of zinc in concentrates are oxidized to zinc oxide, but at the roasting temperatures around 10% of the zinc reacts with the iron impurities of the zinc sulfide concentrates to form zinc ferrite. A byproduct of roasting is sulfur dioxide, which is further processed into sulfuric acid, a commodity.HP Pavilion DV4-1313DX Battery

The linked refinery flow sheet shows a schematic of Noranda's eastern Canadian zinc roasting operation[5]

The process of roasting varies based on the type of roaster used. There are three types of roasters: multiple-hearth, suspension, and fluidized-bed.HP Pavilion DV4-1313TU Battery

Multiple-hearth roaster

In a multiple-hearth roaster, the concentrate drops through a series of 9 or more hearths stacked inside a brick-lined cylindrical column. As the feed concentrate drops through the furnace, it is first dried by the hot gases passing through the hearths and then oxidized to produce calcine.HP Pavilion DV4-1313TX Battery

The reactions are slow and can be sustained only by the addition of fuel. Multiple hearth roasters are unpressurized and operate at about 690 °C (1,270 °F). Operating time depends upon the composition of concentrate and the amount of the sulfur removal required. Multiple hearth roasters have the capability of producing a high-purity calcine.HP Pavilion DV4-1314TU Battery

Suspension roaster

In a suspension roaster, the concentrates are blown into a combustion chamber very similar to that of a pulverized coal furnace. The roaster consists of a refractory-lined cylindrical steel shell, with a large combustion space at the top and 2 to 4 hearths in the lower portion, similar to those of a multiple hearth furnace.HP Pavilion DV4-1314TX Battery

 Additional grinding, beyond that required for a multiple hearth furnace, is normally required to ensure that heat transfer to the material is sufficiently rapid for the desulfurization and oxidation reactions to occur in the furnace chamber. Suspension roasters are unpressurized and operate at about 980 °C(1,800 °F).HP Pavilion DV4-1315TU Battery

Fluidized-bed roaster

In a fluidized-bed roaster, finely ground sulfide concentrates are suspended and oxidized in a feedstock bed supported on an air column. As in the suspension roaster, the reaction rates for desulfurization are more rapid than in the older multiple-hearth processes.HP Pavilion DV4-1315TX Battery

Fluidized-bed roasters operate under a pressure slightly lower than atmospheric and at temperatures averaging 1,000 °C (1,830 °F). In the fluidized-bed process, no additional fuel is required after ignition has been achieved. The major advantages of this roaster are greater throughput capacities, greater sulfur removal capabilities, and lower maintenance.HP Pavilion DV4-1316TU Battery

Electrolysis process

The electrolysis process, also known as the hydrometallurgical process, Roast-Leach-Electrowin (RLE) process, or electrolytic process, is more widely used than the pyrometallurgical processes. 

The electrolysis process consists of 4 steps: leaching, purification, electrolysis, and melting and casting.HP Pavilion DV4-1316TX Battery

Leaching

The basic leaching chemical formula that drives this process is:

This is achieved in practice though a process called double leaching. The calcine is first leached in a neutral or slightly acidic solution (of sulfuric acid) in order to leach the zinc out of the zinc oxide. The remaining calcine is then leached in strong sulfuric acid to leach the rest of the zinc out of the zinc oxide and zinc ferrite.HP Pavilion DV4-1317TU Battery

 The result of this process is a solid and a liquid; the liquid contains the zinc and is often called leach product; the solid is called leach residue and contains precious metals (usually lead and silver) which are sold as a by-product. There is also iron in the leach product from the strong acid leach, which is removed in an intermediate step, in the form of goethite, jarosite, and haematite.HP Pavilion DV4-1317TX Battery

 There is still cadmium, copper, arsenic, antimony, cobalt, germanium, nickel, andthallium in the leach product. Therefore it needs to be purified. 

 Purification

The purification process utilizes the cementation process to further purify the zinc. It uses zinc dust and steam to remove copper, cadmium, cobalt, and nickel, which would interfere with the electrolysis process.HP Pavilion DV4-1318TU Battery

 After purification, concentrations of these impurities are limited to less than 0.05 milligram per liter (4×10−7 pound per U.S. gallon). Purification is usually conducted in large agitated tanks. The process takes place at temperatures ranging from 40 to 85 °C (104 to 185 °F), and pressures ranging from atmospheric to 2.4 atm (240 kPa) (absolute scale). The by-products are sold for further refining.HP Pavilion DV4-1318TX Battery

The zinc sulfate solution must be very pure for electrowinning to be at all efficient. Impurities can change the decomposition voltage enough to where the electrolysis cell produces largely hydrogen gas rather than zinc metal. 

 Electrolysis

Zinc is extracted from the purified zinc sulfate solution by electrowinning, which is a specialized form of electrolysis.HP Pavilion DV4-1319TU Battery

The process works by passing an electric current through the solution in a series of cells. This causes the zinc to deposits on the cathodes (aluminium sheets) and oxygen to form at the anodes. Sulfuric acid is also formed in the process and reused in the leaching process.HP Pavilion DV4-1319TX Battery

 Every 24 to 48 hours, each cell is shut down, the zinc-coated cathodes are removed and rinsed, and the zinc is mechanically stripped from the aluminium plates. 

Electrolytic zinc smelters contain as many as several hundred cells. A portion of the electrical energy is converted into heat, which increases the temperature of the electrolyte.HP Pavilion DV4-1320CA Battery

Electrolytic cells operate at temperature ranges from 30 to 35 °C (86 to 95 °F) and at atmospheric pressure. A portion of the electrolyte is continuously circulated through the cooling towers both to cool and concentrate the electrolyte through evaporation of water. The cooled and concentrated electrolyte is then recycled to the cells.HP Pavilion DV4-1320TX Battery

 This process accounts for approximately one-third of all the energy usage when smelting zinc. 

There are two common processes for electrowinning the metal: the low current density process, and the Tainton high current density process. The former uses a 10% sulfuric acid solution as the electrolyte, with current density of 270–325 amperes per square meter.HP Pavilion DV4-1321TX Battery

The latter uses 22–28% sulfuric acid solution as the electrolyte with a current density of about 1,000 amperes per square metre. The latter gives better purity and has higher production capacity per volume of electrolyte, but has the disadvantage of running hotter and being more corrosive to the vessel in which it is done.HP Pavilion DV4-1322TX Battery

In either of the electrolytic processes, each metric ton of zinc production expends about 3,900 kW·h (14 GJ) of electric power. 

 Melting and casting

The final step is to melt the cathodes in an induction furnace. It is then either cast into pure zinc (99.995% pure) ingots or alloyed and cast into ingots.HP Pavilion DV4-1322US Battery

Pyrometallurgical processes

There are also several pyrometallurgical processes that reduce zinc oxide using carbon, then distil the metallic zinc from the resulting mix in an atmosphere of carbon monoxide. The major downfall of any of the pyrometallurgical process is that it is only 98% pure; a standard composition is 1.3% lead, 0.2% cadmium, 0.03% iron, and 98.5% zinc.HP Pavilion DV4-1323TX Battery

This may be pure enough for galvanization, but not enough for die casting alloys, which requires special high-grade zinc (99.995% pure).[7]In order to reach this purity the zinc must be refined.HP Pavilion DV4-1324TX Battery

The four types of commercial pyrometallurgical processes are the Belgian-type horizontal retort process, the New Jersey Zinc continuous vertical-retort process, theblast furnace process and the St. Joseph Minerals Corporation's (electrothermic) process.HP Pavilion DV4-1325TX Battery

St. Joseph Mineral Company (electrothermic) process

This process was developed by the St. Joseph Mineral Company in 1930, and is the only pyrometallurgical process still used in the US to smelt zinc. The advantage of this system is that it is able to smelt a wide variety of zinc-bearing materials, including electric arc furnace dust.HP Pavilion DV4-1326TX Battery

The disadvantage of this process is that it is less efficient than the electrolysis process. 

The process begins with a downdraft sintering operation. The sinter, which is a mixture of roaster calcine and EAF calcine, is loaded onto a gate type conveyor and then combustions gases are pumped through the sinter.HP Pavilion DV4-1327TX Battery

The carbon in the combustion gases react with some the impurities, such as lead, cadmium, and halides. These impurities are driven off into filtration bags. The sinter after this process, called product sinter, usually has a composition of 48% zinc, 8% iron, 5% aluminium, 4% silicon, 2.5% calcium, and smaller quantities of magnesium, lead, and other metals.HP Pavilion DV4-1328TX Battery

 The sinter product is then charged with coke into an electric retort furnace. A pair of graphite electrodes from the top and bottom furnace produce current flow through the mixture. The coke provides electrical resistance to the mixture in order to heat the mixture to 1,400 °C (2,550 °F) and produce carbon monoxide.HP Pavilion DV4-1329TX Battery

These conditions allow for the following chemical reaction to occur:

The zinc vapour and carbon dioxide pass to a vacuum condenser, where zinc is recovered by bubbling through a molten zinc bath. Over 95% of the zinc vapour leaving the retort is condensed to liquid zinc. The carbon dioxide is regenerated with carbon, and the carbon monoxide is recycled back to the retort furnace.HP Pavilion DV4-1330TX Battery

Blast furnace process

This process was developed by the Imperial Smelting Corporation at Avonmouth, England, in order to increase production, increase efficiency, and decrease labour and maintenance costs. L. J. Derham proposed using a spray of molten lead droplets to rapidly chill and absorb the zinc vapour, despite the high concentration of carbon dioxide.HP Pavilion DV4-1331TX Battery

The mixture is then cooled, where the zinc separates from the lead. The first plant using this design opened up in 1950. One of the advantages of this process is that it can co-produce lead bullion and copper dross. In 1990, it accounted for 12% of the world's zinc production.HP Pavilion DV4-1332TX Battery

The process starts by charging solid sinter and heated coke into the top of the blast furnace. Preheated air at 190 to 1,050 °C (370 to 1,920 °F) is blown into the bottom of the furnace. Zinc vapour and sulfides leave through the top and enter the condenser. Slag and lead collect at the bottom of the furnace and are tapped off regularly.HP Pavilion DV4-1365DX Battery

The zinc is scrubbed from the vapour in the condenser via liquid lead. The liquid zinc is separated from the lead in the cooling circuit. Approximately 5,000 metric tons (5,500 short tons) of lead are required each year for this process, however this process recovers 25% more lead from the starting ores than other processes.HP Pavilion DV4-1400 CTO Battery

New Jersey Zinc continuous vertical retort

The New Jersey Zinc process is no longer used to produce primary zinc in the U.S., Europe and Japan, however it still is used to treat secondary operations. This processes peaked in 1960, when 5% of the world production was done by this process. A modified version of this process is still used at Huludao, China, which produced 65,000 metric tons per year.HP Pavilion DV4-1404TX Battery

This process begins by roasting concentrates that are mixed with coal and briquetted in two stages. The briquettes are then heated in an autogenous coker at 700 °C(1,292 °F) and then charged into the retort. There are three reasons to briquette the calcine: to ensure free downward movement of the charge; to permit heat transfer across a practical size cross-section;HP Pavilion DV4-1405TX Battery

 to allow adequate porosity for the passage of reduced zinc vapour to the top of the retort. The reduced zinc vapour that is collected at the top of the retort is then condensed to a liquid.

Overpelt improved upon this design by using only one large condensation chamber, instead of many small ones, as it was originally designed. This allowed for the carbon monoxide to be recirculated into the furnaces for heating the retorts.HP Pavilion DV4-1406TX Battery

This process was licensed to the Imperial Smelting Company (ISC), in Avonmouth, England, which had a large vertical retort (VR) plant in production for many years. It was used until the mid 1970s when it was superseded by the company's Imperial Smelting Furnace (ISF) plant. The VR plant was demolished in 1975.HP Pavilion DV4-1407TX Battery

Belgian-type horizontal retort process

This process was the main process used in Britain from the mid-19th century until 1951. The process was very inefficient as it was designed as a small scale batch operation. Each retort only produced 40 kilograms (88 lb) so companies would put them together in banks and used one large gas burner to heat all of them.HP Pavilion DV4-1408TX Battery

The Belgian process requires redistillation to remove impurities of lead, cadmium, iron, copper, and arsenic.

Although some zinc artifacts appear to have been made during classical antiquity in Europe,[9] the first production of zinc in quantity seems to have been in Indiaand China.HP Pavilion DV4-1409TX Battery

 In India, zinc was produced at Zawar from the 12th to the 18th centuries. The sphalerite ore found here was presumably converted to zinc oxide via roasting, although no archaeological evidence of this has been found. Smelting is thought to have been done in sealed cylindrical clay retorts which were packed with a mixture of roasted ore,HP Pavilion DV4-1413LA Battery

 dolomite, and an organic material, perhaps cow dung, and then placed vertically in a furnace and heated to around 1100 °C. Carbon monoxideproduced by the charring of the organic material would have reduced the zinc oxide to zinc vapour, which then liquefied in a conical clay condenser at the bottom of the retort, dripping down into a collection vessel.HP Pavilion DV4-1414LA Battery

 Over the period 1400–1800, production is estimated to have been about 200 kg/day.[11] Zinc was also smelted in China from the mid-sixteenth century on.[12]

Large-scale zinc production in Europe began with William Champion, who patented a zinc distillation process in 1738.HP Pavilion DV4-1416LA Battery

In Champion's process, zinc ore (in this case, the carbonate, ZnCO3) was sealed in large reduction pots with charcoal and heated in a furnace. The zinc vapor then descended through an iron condensing pipe until reaching a water-filled vessel at the bottom.HP Pavilion DV4-1425LA Battery

Champion set up his first zinc works in Bristol, England, but soon expanded to Warmley and by 1754 had built four zinc furnaces there.[15] Although Champion succeeded in producing about 200 tons of zinc,[15] his business plans were not successful and he was bankrupt by 1769.[14] However, zinc smelting continued in this area until 1880.[HP Pavilion DV4T Battery

Early European zinc production also took place in Silesia, in Carinthia, and in Liège, Belgium. In the Carinthian process, used in works established in 1798 by Bergrath Dillinger, a wood-fueled furnace heated a large number of small vertical retorts,[18] and zinc vapor then dropped through a ceramic pipe into a common condensation chamber below.HP Pavilion DV4T-1000 CTO Battery

This process was out of use by 1840. The Belgian and Silesian processes both used horizontal retorts.[19] In Silesia, Johann Ruhberg built a furnace to distill zinc in 1799, at first using pots but later changing to flat-bottomed retorts called "muffles", attached to horizontal tubes bent downwards in which the zinc condensed.HP Pavilion DV4T-1100 CTO Battery

The Silesian process eventually merged with the Belgian process. This process, developed by Jean-Jacques Daniel Dony, was introduced 1805–1810, and used retorts with a cylindrical cross-section. Condensers were horizontal clay tubes extending from the ends of the retorts.HP Pavilion DV4T-1200 CTO Battery

The merged "Belgo-Silesian" horizontal retort process was widely adopted in Europe by the third quarter of the 19th century, and later in the United States. 

Experimental attempts to extract zinc via electrolysis begun in the 19th century, but the only commercially successful application before 1913 was a process, used inGreat Britain and Austria,HP Pavilion DV4T-1200SE CTO Battery

where zinc and chlorine were co-produced by electrolysis of an aqueous zinc chloride solution.[21] The Anaconda Copper Company, atAnaconda, Montana, and the Consolidated Mining and Smelting Company, at Trail, British Columbia, both built successful electrolytic plants in 1915 using the currently used zinc sulfate process.HP Pavilion DV4T-1300 CTO Battery

This method has continued to grow in importance and in 1975 accounted for 68% of world zinc production. 

The continuous vertical retort process was introduced in 1929 by the New Jersey Zinc Company. This process used a retort with silicon carbide walls, around 9 meters high and with a cross section of 2 by 0.3 meters.HP Pavilion DV4T-1300SE CTO Battery

The walls of the retort were heated to 1300 °C and briquettes consisting of sintered zinc ore, coke, coal, and recycled material were fed into the top of the retort. Gaseous zinc was drawn off from the top of the column and, after a 20-hour journey through the retort, spent briquettes were removed from the bottom.HP Pavilion DV4T-1400 CTO Battery

To condense the gaseous zinc, the company first used a simple brick chamber with carborundum baffles, but efficiency was poor. During the 1940s a condenser was developed which condensed the zinc vapor on a spray of liquid zinc droplets, thrown up by an electrical impeller.HP Pavilion DV4Z Battery

The electrothermic process, developed by the St. Joseph's Lead Company, was somewhat similar.  The first commercial plant using this process was built in 1930 at the present site of Josephtown, Pennsylvania. The electrothermic furnace was a steel cylinder around 15 meters high and 2 meters in diameter, lined with firebrick.HP Pavilion DV4Z-1000 CTO Battery

A mixture of sintered ore and coke was fed into the top of the furnace, and a current of 10,000–20,000 amperes, at a potential difference of 240 volts, was applied between carbon electrodes in the furnace, raising the temperature to 1200–1400 °C. An efficient condenser was devised for this process from 1931–1936;HP Pavilion DV4Z-1100 CTO Battery

it consisted of a bath of liquid zinc which the exhaust gases were drawn through by suction. The zinc content of the gas stream was absorbed into the liquid bath. 

The blast-furnace process was developed starting in 1943 at Avonmouth, England by the Imperial Smelting Corporation. It uses a spray of molten lead droplets to condense the zinc vapor.HP Pavilion DV4Z-1200 CTO Battery

Zinc deficiency is insufficient zinc to meet the needs of biological organisms. It can occur in both plants and animals. Zinc deficient soil is soil in which there is insufficient zinc to allow plants to grow normally.

Prevalence

In fact, one-third of the world population is at risk of zinc deficiency, ranging from 4 to 73% depending on the country.HP Pavilion DV4 Battery

 Zinc deficiency is the fifth leading risk factor for disease in the developing world. Providing micronutrients, including zinc, to humans is one of the four quick-win solutions to major global problems identified in the Copenhagen Consensus from an international panel of distinguished economists.HP Pavilion DV4-1000 Battery

Conservative estimates suggest that 25% of the world's population is at risk of zinc deficiency.

Causes

Hypozincemia is usually a nutritional deficiency, but can also be associated with malabsorption, diarrhea, acrodermatitis enteropathica, chronic liver disease, chronic renal disease, sickle-cell disease, diabetes, malignancy, and other chronic illnesses.HP Pavilion DV4-1000EA Battery

 It can also occur after bariatric surgery.

Zinc deficiency is typically the result of inadequate dietary intake of zinc, disease states that promote zinc losses, or physiological states that require increased zinc. Populations that consume primarily plant based diets that are low in bioavailable zinc often have zinc deficiencies.HP Pavilion DV4-1000ET Battery

Diseases or conditions that involve intestinal malabsorption promote zinc losses. Fecal losses of zinc caused by diarrhea are one contributing factor, often common in developing countries. Changes in intestinal tract absorbability and permeability due, in part, to viral, protozoal, and bacteria pathogens may also encourage fecal losses of zinc.HP Pavilion DV4-1001 Battery

Physiological states that require increased zinc include periods of growth in infants and children as well as in mothers during pregnancy. 

 Signs and symptoms

Signs of zinc deficiency include hair loss, skin lesions, diarrhea, and wasting of body tissues. A lack of zinc can contribute to acne.HP Pavilion DV4-1001AX Battery

Eyesight, taste, smell and memory are also connected with zinc. A deficiency in zinc can cause malfunctions of these organs and functions. Congenital abnormalities causing zinc deficiency may lead to a disease called acrodermatitis enteropathica.

One easily recognized sign which may be caused by zinc deficiency is white spots, bands, or lines on fingernails (leukonychia).HP Pavilion DV4-1001TU Battery

An occasional white spot is usually evidence that the immune system overcame a bacterial or some other systemic infection, and is a positive, not negative sign. Some women may have multiple parallel white bands or lines on the fingernails marking menstrual cycles when marginal zinc deficiency was present.HP Pavilion DV4-1001TX Battery

Anorexia

Zinc deficiency may cause a decrease in appetite which can degenerate into anorexia or anorexia nervosa. Appetite disorders, in turn, causemalnutrition and, notably, inadequate zinc intake. Anorexia itself is a cause of zinc deficiency, thus leading to a vicious cycle: the worsening of anorexia worsens the zinc deficiency.HP Pavilion DV4-1002 Battery

The use of zinc in the treatment of anorexia has been advocated since 1979 by Bakan. At least 15 trials showed that zinc improved weight gain in anorexia. A 1994 randomized, double-blind, placebo-controlled trial showed that zinc (14 mg per day) doubled the rate of body mass increase in the treatment of anorexia nervosa (AN).HP Pavilion DV4-1002AX Battery

Deficiency of other nutrients such as tyrosine and tryptophan (precursors of the monoamine neurotransmitters norepinephrine and serotonin, respectively), as well as vitamin B1 (thiamine) could contribute to this phenomenon of malnutrition-induced malnutrition.HP Pavilion DV4-1002TU Battery

Cognitive and motor function impairment

Cognitive and motor function may also be impaired in zinc deficient children. Zinc deficiency can interfere with many organ systems especially when it occurs during a time of rapid growth and development when nutritional needs are high, such as during infancy.HP Pavilion DV4-1002TX Battery

In animal studies, rats who were deprived of zinc during early fetal development exhibited increased emotionality, poor memory, and abnormal response to stress which interfered with performance in learning situations. Zinc deprivation in monkeys showed that zinc deficient animals were emotionally less mature, and also had cognitive deficits indicated by their difficulty in retaining previously learned problems and in learning new problems.HP Pavilion DV4-1003AX Battery

Human observational studies show weaker results. Low maternal zinc status has been associated with less attention during the neonatal period and worse motor functioning.In some studies, supplementation has been associated with motor development in very low birth weight infants and more vigorous and functional activity in infants and toddlers.HP Pavilion DV4-1003TU Battery

Diarrhea and pneumonia

Zinc deficiency contributes to an increased incidence and severity of diarrhea and pneumonia. Studies have shown that zinc treatment results in a 25 percent reduction in duration of acute diarrhea and a 40 percent reduction in treatment failure or death in persistent diarrhea.HP Pavilion DV4-1003TX Battery

The studies determined that a ten-day therapy of zinc treatment can considerably reduce the duration and severity of diarrheal episodes, decrease stool output, and lessen the need for hospitalization. Zinc may also prevent future diarrhea episodes for up to three months.HP Pavilion DV4-1004AX Battery

The current World Health Organization recommendation for diarrhea control includes the use of 20 mg per day of zinc supplementation for 10 to 14 days (10 mg per day for infants under the age of six months).[21] A zinc taste test may have potential for diagnosing deficiency.HP Pavilion DV4-1004TU Battery

High dose of zinc, 30 mg 1-3 times a day, prevents dysmenorrhea. 

Zinc deficiency during pregnancy can negatively affect both the mother and fetus. Animal studies indicate that maternal zinc deficiency can upset both the sequencing and efficiency of the birth process.HP Pavilion DV4-1004TX Battery

An increased incidence of difficult and prolonged labor, hemorrhage, uterine dystocia and placental abruption has been documented in zinc deficient animals. These effects may be mediated by the defective functioning of estrogen via the estrogen receptor, which contains a zinc finger protein.HP Pavilion DV4-1005TX Battery

A review of pregnancy outcomes in women with acrodermatitis enteropathica, reported that out of every seven pregnancies, there was one abortion and two malfunctions, suggesting the human fetus is also susceptible to the teratogenic effects of severe zinc deficiency.HP Pavilion DV4-1006TX Battery

 However, a review on zinc supplementation trials during pregnancy did not report a significant effect of zinc supplementation on neonatal survival. 

 Vitamins A and D

Plasma zinc levels have been found to be dependent upon vitamins A and D.HP Pavilion DV4-1007TX Battery

This suggests that a Vitamin A or D deficiency could cause a secondary zinc deficiency and that for treatment of zinc deficiency one should ensure adequate vitamin A and D intake.

 Hunger

The influence of zinc on hunger is complex and likely depends upon the status of other nutrients, the developmental stage of the animal, and percentage body fat.HP Pavilion DV4-1008TX Battery

Some research groups have argued for a role of zinc deficiency decreasing appetite, while others have shown zinc ingestion can reduce feelings of hunger by increasing leptin levels. There is evidence that the way zinc influences hunger depends on the sodium/osmotic status of the organism,HP Pavilion DV4-1009TX Battery

with low sodium/low zinc levels increasing hunger and high sodium/low zinc levels decreasing it. An organism with a low level of zinc has an increased susceptibility to hypoosmotic stress and cell rupture. Thus if the osmotic pressure is too low the organism may be inclined to eat to raise osmolality and prevent osmotic shock.HP Pavilion DV4-1010TX Battery

It should be noted that zinc is known to affect osmolality by increasing sodium retention.

In rats, the "first visible sign" of zinc deficiency is a decreased appetite. 

 Treatment

Zinc supplementation has been shown to reduce diarrhea prevalence and mortality in children younger than 5 years of age.HP Pavilion DV4-1011TX Battery

To combat zinc deficiency, five intervention strategies can be used:

  • Supplementation using medicines
  • Food fortification through the incorporation of zinc additives in food
  • Dietary modification/diversificationHP Pavilion DV4-1012TX Battery
  • Genetic biofortification through plant breeding
  • Agronomic biofortification through zinc fertilization.

These five intervention strategies may be used individually or in combination, depending on the setting, target group and degree of zinc deficiency.HP Pavilion DV4-1013TX Battery

The amount of zinc absorbed by the human body is a function of dietary intake of both zinc and phytate (a phosphate storage compound that chelates zinc), because the ratio between these two substances affects the bioavailability of zinc. Meeting the needs for absorbed zinc requires an increase in the zinc content and/or a decrease in the phytate content.HP Pavilion DV4-1014NR Battery

Plants, crops, and soils

Zinc is an essential micronutrient needed not only by people but also by crops. Almost half of the world’s cereal crops are deficient in zinc, leading to poor crop yields.Many agricultural countries around the world are affected by zinc deficiencies.HP Pavilion DV4-1014TX Battery

In China, zinc deficiency occurs on around half of the agricultural soils, affecting mainly rice and maize.

In India, zinc-deficient soils occupy almost 50% of the agricultural area and are a critical constraint on yield, but crops are highly responsive to zinc fertilization.HP Pavilion DV4-1015TX Battery

In Turkey, major yield and quality benefits in wheat have been obtained with the widespread use of zinc fertilizers, where half of the cereal growing land is zinc-deficient.

Research has shown that areas with zinc-deficient soils are often regions with widespread zinc deficiency in humans.HP Pavilion DV4-1015TX Battery

A basic knowledge of the dynamics of Zn in soils, understanding of the uptake and transport of Zn in plant systems and characterizing the response of plants to Zn deficiency are essential steps in achieving sustainable solutions to the problem of Zn deficiency in plants and humans (Zinc in soils and crop nutrition), International Fertilizer Industry Association (IFA)and International Zinc Association (IZA).)1016tx-battery-13368.htm" title="HP PAVILION DV4-1016TX laptop battery">HP Pavilion DV4-1016TX Battery

 Fertilization

Experiments show that soil and foliar application of zinc fertilizer can effectively reduce the phytate:zinc ratio in grain. People who eat bread prepared from zinc enriched wheat show a significant increase in serum zinc, suggesting that the zinc fertilizer strategy may be a viable commercial approach to address zinc deficiencies in humans.HP Pavilion DV4-1017TX Battery

Where zinc deficiency is a limiting factor, zinc fertilization can increase crop yields. Balanced crop nutrition supplying all essential nutrients, including zinc, is a cost effective management strategy. Even with zinc-efficient varieties, zinc fertilizers are needed when the available zinc in the topsoil becomes depleted.HP Pavilion DV4-1018TX Battery

Plant breeding, including modern biotechnology, can improve:

Zinc uptake capacity of plants under soil conditions with low chemical availability of zinc; Zinc translocation, thus elevating zinc content in edible crop parts rather than the rest of the plant; Zinc bioavailability.HP Pavilion DV4-1019TX Battery

For optimal efficiency, zinc-efficient genotypes should be associated with complementary soil crop management (including fertilization) to ensure adequate zinc uptake by roots and thus enhance zinc nutrition of crops and humans

 Turkey

Central Anatolia, in Turkey, was a region with zinc-deficient soils and widespread zinc deficiency in humans.HP Pavilion DV4-1020TX Battery

In 1993, a research project found that yields could be increased by 6 to 8-fold and children nutrition dramatically increased through zinc fertilization.

Through a partnership with Cukurova University, the State and the private company TOROS Agri Industry Group, zinc was added to fertilizers.HP Pavilion DV4-1020US Battery

 While the product was initially made available at the same cost, the results were so convincing that Turkish farmers significantly increased the use of the zinc-fortified fertilizer (1 per cent of zinc) within a few short years, despite the repricing of the products to reflect the added value of the content.HP Pavilion DV4-1021TX Battery

Today, nearly 10 years after the identification of the zinc deficiency problem, the total amount of zinc-containing compound fertilizers produced and applied in Turkey reached a record level of 300,000 tonnes per annum.HP Pavilion DV4-1022TX Battery

It is estimated that the economic benefits associated with the application of Zn-fertilizers on Zn deficient soils in Turkey is around US$ 100 million per year. Zinc deficiency in children has been dramatically reduced.HP Pavilion DV4-1023TX Battery

Such a policy could be easily replicated around the world in the many zinc-deficient countries.HP Pavilion DV4-1024TX Battery,HP Pavilion DV4-1025TX Battery,HP Pavilion DV4-1026TX Battery,HP Pavilion DV4-1027TX Battery,HP Pavilion DV4-1028TX Battery,HP Pavilion DV4-1028US Battery,HP Pavilion DV4-1029TX Battery,HP Pavilion DV4-1030EE Battery,HP Pavilion DV4-1030EI Battery

 

Partager cet article

Repost 0
Published by batterys - dans Laptop Battery
commenter cet article

commentaires