Gold has been recovered from its ores in many ways throughout the centuries. These ways range from the rocker or long tom of the California Forty-Niner and the noisy stamp mill of the 19th century to modern methods of leaching with cyanide.
Any method of treating ores of gold must take advantage of the natural characteristics of the metal. Cyanide solution which is not like the majority of other liquids is able to dissolve gold, and this way, is used in the processing of gold ore. Cyanide slowly attacks fine particles of gold and ultimately dissolves them when in solution and in the presence of oxygen. It is strange, but fortunate due to the fact that cyanide is extremely toxic, that a weak cyanide solution attacks the gold particles faster than a strong solution.
It is necessary that the gold first be freed from the gangue rock that is worthless which surrounds it for the cyanide to attack the gold particles because cyanide will not attack or dissolve most other minerals.
In general, the process of cyanide is very efficient. A gold ore that contains less than one gram of gold per tonne can in some cases (and depending on the price of gold), be treated profitably. A modern cyanide mill extracts or recovers 95% to 98% of the gold which is in the ore.
Lime and cyanide are added to the ore pulp in the grinding circuit of a cyanide mill. The lime has a variety of functions: it protects the cyanide from being destroyed by chemicals that occur naturally called cyanicides and improves the settlement rate of the pulp in the thickening stage.
The actual dissolution of the gold (cyanidation) begins in the grinding step. Cyanide and lime solutions are introduced here, where newly liberated gold particles are being constantly polished by the grinding action and the friction is what heats the solutions. From 30% to 70% of the gold may be dissolved during the grinding process depending on the ore and the fineness of the grind.
Additional time is required to place the balance of the liberated gold into solution. This is done by pumping the pulp that bears gold to a large amount of mixing tanks, which are known as agitators. Here the pulp is aerated either by compressed air or mechanically, or by a combination of both, for a predetermined period of time. This varies anywhere from 24 to 48 hours.
The 1980s saw a quick expansion in gold production from low-grade oxide deposits around the world. That expansion would not have been able to occur without the development of a new, low-cost method of recovering the gold. That process is called heap leaching.
Heap leaching avoids most of the previous steps, and does not even require that a mill be built, making it a very inexpensive method of processing ore. Here, broken ore is heaped onto a thick polyethylene sheet, which is called a liner, and then dilute cyanide solution is sprinkled on top of the heap. The gold is dissolved as the solution trickles down through the ore. Before the heap is constructed, the polyethylene liner is laid down in a certain way that the cyanide solution will drain to a central point. From here the gold-laden solution is channeled into a pond which is made by man.
Tuesday, December 23, 2008
REFINING OF PETROLEUM
Petroleum is a complex mixture of organic liquids called crude oil and natural gas, which occurs naturally in the ground and was formed millions of years ago. Crude oil varies from oilfield to oilfield in colour and composition, from a pale yellow low viscosity liquid to heavy black 'treacle' consistencies.
Crude oil and natural gas are extracted from the ground, on land or under the oceans, by sinking an oil well and are then transported by pipeline and/or ship to refineries where their components are processed into refined products. Crude oil and natural gas are of little use in their raw state; their value lies in what is created from them: fuels, lubricating oils, waxes, asphalt, petrochemicals and pipeline quality natural gas.
An oil refinery is an organised and coordinated arrangement of manufacturing processes designed to produce physical and chemical changes in crude oil to convert it into everyday products like petrol, diesel, lubricating oil, fuel oil and bitumen.
As crude oil comes from the well it contains a mixture of hydrocarbon compounds and relatively small quantities of other materials such as oxygen, nitrogen, sulphur, salt and water. In the refinery, most of these non - hydrocarbon substances are removed and the oil is broken down into its various components, and blended into useful products.
Natural gas from the well, while principally methane, contains quantities of other hydrocarbons - ethane, propane, butane, pentane and also carbon dioxide and water. These components are separated from the methane at a gas fractionation plant.
Crude oil and natural gas are extracted from the ground, on land or under the oceans, by sinking an oil well and are then transported by pipeline and/or ship to refineries where their components are processed into refined products. Crude oil and natural gas are of little use in their raw state; their value lies in what is created from them: fuels, lubricating oils, waxes, asphalt, petrochemicals and pipeline quality natural gas.
An oil refinery is an organised and coordinated arrangement of manufacturing processes designed to produce physical and chemical changes in crude oil to convert it into everyday products like petrol, diesel, lubricating oil, fuel oil and bitumen.
As crude oil comes from the well it contains a mixture of hydrocarbon compounds and relatively small quantities of other materials such as oxygen, nitrogen, sulphur, salt and water. In the refinery, most of these non - hydrocarbon substances are removed and the oil is broken down into its various components, and blended into useful products.
Natural gas from the well, while principally methane, contains quantities of other hydrocarbons - ethane, propane, butane, pentane and also carbon dioxide and water. These components are separated from the methane at a gas fractionation plant.
PLASTIC RECYCLING
There are four options available at the end of a plastic product's life: mechanical recycling, chemical recycling, energy recovery and landfill. In New Zealand, landfill is the prevalent destination for plastic products, with 18% of plastic packaging now being diverted through private and public recycling operations
The material collected by territorial authorities and recycling companies is used for mechanical recycling. This process involves: material collection - the plastics destined for recycling need to be collected; this may be from a manufacturing site, a commercial operation seeking to dispose of bulk packaging, such as pallet wrap, "drop off" points at schools, or from houses, from a kerbside collection
transport to the recycling centre , sorting into types that can be re-processed together, and either , baling for export or , cleaning to remove dirt and other contaminants normally this is done by cutting the plastics into small flakes and putting these flakes through a washing and drying process , the flakes are then melted and extruded (squirted) into thin lines and then chopped into granules , reuse - the granules, or pellets, can then be used to make new plastic products.
Innovative techniques in the energy recovery and materials recovery area are beginning to appear in Europe, the US and Japan. While the relatively small volumes of recyclable material available in this country may make such developments too expensive to establish here, the local industry continues to monitor, investigate and commit resources to seeking a technology, or technologies
The material collected by territorial authorities and recycling companies is used for mechanical recycling. This process involves: material collection - the plastics destined for recycling need to be collected; this may be from a manufacturing site, a commercial operation seeking to dispose of bulk packaging, such as pallet wrap, "drop off" points at schools, or from houses, from a kerbside collection
transport to the recycling centre , sorting into types that can be re-processed together, and either , baling for export or , cleaning to remove dirt and other contaminants normally this is done by cutting the plastics into small flakes and putting these flakes through a washing and drying process , the flakes are then melted and extruded (squirted) into thin lines and then chopped into granules , reuse - the granules, or pellets, can then be used to make new plastic products.
Innovative techniques in the energy recovery and materials recovery area are beginning to appear in Europe, the US and Japan. While the relatively small volumes of recyclable material available in this country may make such developments too expensive to establish here, the local industry continues to monitor, investigate and commit resources to seeking a technology, or technologies
POLYMERS
Natural Polymers
Natural polymers are common in animals and plants. Much living tissue is based on polymers – for example proteins in animals and carbohydrates in plants. A lot of our food is based on polymers – for example, fibre, grain and meeat. Plants and animals also produce non-living materials based on polymers.
These are usually produced as fibres and then have to be processed to produce materials such as threads and fabrics. These include: rubber products, gums and resins, clays, bitumens and waxes, hoof and horns, casein products and cellulose products
Synthetic Polymers
While natural polymers are still part of the plastics world nowadays the word plastic is generally reserved for syn¬thetic plastic materials. Synthetic polymers are made mainly from petroleum (crude oil) or natural gas. This is processed in an oil refinery to produce basic chemicals known as monomers. The monomers are then turned into polymers.
Some polymers are turned into solid plastics material, and others into textile fibres. Some can be turned into either, depending on how they are processed. In some cases synthetic plastics are mixed with, or used in combination with, natural materials. Most of this educational resource is based around the synthetic plastics that originate from the petrochemical industry.
Natural polymers are common in animals and plants. Much living tissue is based on polymers – for example proteins in animals and carbohydrates in plants. A lot of our food is based on polymers – for example, fibre, grain and meeat. Plants and animals also produce non-living materials based on polymers.
These are usually produced as fibres and then have to be processed to produce materials such as threads and fabrics. These include: rubber products, gums and resins, clays, bitumens and waxes, hoof and horns, casein products and cellulose products
Synthetic Polymers
While natural polymers are still part of the plastics world nowadays the word plastic is generally reserved for syn¬thetic plastic materials. Synthetic polymers are made mainly from petroleum (crude oil) or natural gas. This is processed in an oil refinery to produce basic chemicals known as monomers. The monomers are then turned into polymers.
Some polymers are turned into solid plastics material, and others into textile fibres. Some can be turned into either, depending on how they are processed. In some cases synthetic plastics are mixed with, or used in combination with, natural materials. Most of this educational resource is based around the synthetic plastics that originate from the petrochemical industry.
MAKING OF PLASTICS
The raw material for plastics is crude oil, a complex mixture of thousands of compounds. To become useful, it must be processed. Around 4% of the world’s production is turned into plastics.Because the compounds in crude oil, have different masses, and therefore boil at different temperatures, it is possible to separate them by a process known as fractional distillation. The mixture is separated into fractions, not into individual compounds. Fractions contain a mixture of compounds whose boiling temperatures are similar.
Cracking breaks large molecules into smaller ones which are more useful - and therefore of greater value. For example, very high boiling point fractions are cracked to produce gasoline and gas oil fractions. Today most cracking uses catalysts, but some heat treatment still occurs.
A feature central to all plastics is that they are constructed from polymers or macromolecules. This applies to both natural and synthetic plastics. A polymer is a long chain molecule consisting of many (usually thousands) of small units called monomers joined end to end. The relationship between polymers and monomers is that of a chain being made up of many individual links.
Reforming changes the internal structure of molecules to produce different compounds with a greater usefulness – and therefore higher value. By altering conditions – such as temperature, pressures and the catalyst – cracking and reforming techniques can now be controlled to produce exactly the blend of compounds which will be most useful at a particular time.
At the heart of all plastics manufacture is synthesis (or joining together). Monomers are joined or synthesised together to form polymers, this process is called polymerisation.
Cracking breaks large molecules into smaller ones which are more useful - and therefore of greater value. For example, very high boiling point fractions are cracked to produce gasoline and gas oil fractions. Today most cracking uses catalysts, but some heat treatment still occurs.
A feature central to all plastics is that they are constructed from polymers or macromolecules. This applies to both natural and synthetic plastics. A polymer is a long chain molecule consisting of many (usually thousands) of small units called monomers joined end to end. The relationship between polymers and monomers is that of a chain being made up of many individual links.
Reforming changes the internal structure of molecules to produce different compounds with a greater usefulness – and therefore higher value. By altering conditions – such as temperature, pressures and the catalyst – cracking and reforming techniques can now be controlled to produce exactly the blend of compounds which will be most useful at a particular time.
At the heart of all plastics manufacture is synthesis (or joining together). Monomers are joined or synthesised together to form polymers, this process is called polymerisation.
Monday, December 22, 2008
THE GOODNESS OF GRAINS
Whole grains provide vitamins, minerals, complex carbohydrates protein, and fiber needed for excellent health. Carbohydrates are required by the body for energy; they are fuel for our brains, muscles, and internal organs. Our bodies do not store most of the calories from carbs (unless, of course, you eat entirely too much food for your activity level)--they store only the calories from fat!--so we must replace these vital calories every day. Our bodies burn the calories from carbs quickly and efficiently, with only 4 calories per gram of weight (unlike fat, which has 9 calories per gram).
Sucrose, glucose, and fructose, and all refined sugars and syrups are simple carbohydrates. Complex carbohydrates are the starches, including whole grains and starchy vegetables. Starches used to be considered a diet enemy by many “experts,” but today we know it isn’t so. These foods are essentially fat- and cholesterol-free, they’re rich sources of vitamins and minerals, are a terrific source of dietary fiber, and they’re filling. They contribute to maintaining a healthy cholesterol level, protect against some cancers, and contribute significantly to healthy skin and hair.
Whole grains are comprised of three layers--the bran, the germ, and the endosperm. The high nutrient density commonly associated with grains exists only when these three are intact. Most of the grains consumed today in the U.S. and Canada, as well as some other countries, are "refined," meaning the bran and germ layers have been stripped away, taking with them about 80% of the nutrients as well as much of the flavor. Manufacturer's often attempt to "enrich" white flour/white rice products, but they [with inferior sources] restore only a fraction of the vitamins and minerals lost, and none of the taste.
It is recommended that our daily caloric intake be 55-60% from complex carbs. This translates to four or five two- to three-ounce servings every day of fruits and vegetables, and five or six servings of whole grains and legumes. There is no reason to be hungry or feel deprived while maintaining a sound diet and healthy body weight.
Fiber is an essential element that comes from plants. Some fiber helps reduce blood cholesterol, especially LDL (“bad” cholesterol), while other fiber cleans the digestive tract and keeps it functioning efficiently and effectively.
Sucrose, glucose, and fructose, and all refined sugars and syrups are simple carbohydrates. Complex carbohydrates are the starches, including whole grains and starchy vegetables. Starches used to be considered a diet enemy by many “experts,” but today we know it isn’t so. These foods are essentially fat- and cholesterol-free, they’re rich sources of vitamins and minerals, are a terrific source of dietary fiber, and they’re filling. They contribute to maintaining a healthy cholesterol level, protect against some cancers, and contribute significantly to healthy skin and hair.
Whole grains are comprised of three layers--the bran, the germ, and the endosperm. The high nutrient density commonly associated with grains exists only when these three are intact. Most of the grains consumed today in the U.S. and Canada, as well as some other countries, are "refined," meaning the bran and germ layers have been stripped away, taking with them about 80% of the nutrients as well as much of the flavor. Manufacturer's often attempt to "enrich" white flour/white rice products, but they [with inferior sources] restore only a fraction of the vitamins and minerals lost, and none of the taste.
It is recommended that our daily caloric intake be 55-60% from complex carbs. This translates to four or five two- to three-ounce servings every day of fruits and vegetables, and five or six servings of whole grains and legumes. There is no reason to be hungry or feel deprived while maintaining a sound diet and healthy body weight.
Fiber is an essential element that comes from plants. Some fiber helps reduce blood cholesterol, especially LDL (“bad” cholesterol), while other fiber cleans the digestive tract and keeps it functioning efficiently and effectively.
SUGAR BLUES
Sugar is a sweet, crystalline carbohydrate typically extracted from sugar cane and sugar beets. It is a non-nutritive empty calorie that robs the body of vitamins and minerals. Refined sugars have many different names, such as granulated (table) sugar, powdered sugar, brown sugar, corn syrup, dextrose, raw sugar, turbinado sugar, and malt. Even much commercial fructose is really pure refined sugar.
Many people believe that sugar is only bad for you when ingested in enormous amounts, when actually "normal" amounts are damaging to the body.
Sugar is addicting. The more you get, the more you want! Some would say it is more addicting than heroin. It used to be only the rich could afford the luxury of sugar, but by 1840 the sugar pushers were handing out free samples. Now, the sugar industries have the largest advertising in the world. Less than 10 years ago the average American consumed something like 153 pounds of sugar a year, with a whopping 24% of their calories coming from sugar. No doubt today the figures would be even more astounding. Many wonderful people are hooked on the stuff, and those who attempt to quit the sugar habit find they have quite a struggle on their hands. Going off sugar, like quitting most drugs, invites withdrawal symptoms. The most common are headaches, chills, and body aches. Sugar, like alcohol, is intoxicating. It creates an imbalance of neurotransmitters in the brain. Mental and emotional disorders are often linked to sugar in the diet.
Only one third of a person’s sugar consumption is purchased as packaged sugar. The rest is consumed in manufactured foods. Almost everything on store shelves has sugar in it, even salt and cigarettes. Some foods are even required to have sugar in them by the FDA. For instance, catsup cannot be called catsup if it does not contain sugar.
When sugar is eliminated from the diet, all foods start to taste better. Taste buds become more sensitive to the natural sweetness of foods. Soon, sugar cravings begin to dwindle and control over ones eating becomes easier and easier. Bodies start feeling better, calmer, and sleep improves.
Many people believe that sugar is only bad for you when ingested in enormous amounts, when actually "normal" amounts are damaging to the body.
Sugar is addicting. The more you get, the more you want! Some would say it is more addicting than heroin. It used to be only the rich could afford the luxury of sugar, but by 1840 the sugar pushers were handing out free samples. Now, the sugar industries have the largest advertising in the world. Less than 10 years ago the average American consumed something like 153 pounds of sugar a year, with a whopping 24% of their calories coming from sugar. No doubt today the figures would be even more astounding. Many wonderful people are hooked on the stuff, and those who attempt to quit the sugar habit find they have quite a struggle on their hands. Going off sugar, like quitting most drugs, invites withdrawal symptoms. The most common are headaches, chills, and body aches. Sugar, like alcohol, is intoxicating. It creates an imbalance of neurotransmitters in the brain. Mental and emotional disorders are often linked to sugar in the diet.
Only one third of a person’s sugar consumption is purchased as packaged sugar. The rest is consumed in manufactured foods. Almost everything on store shelves has sugar in it, even salt and cigarettes. Some foods are even required to have sugar in them by the FDA. For instance, catsup cannot be called catsup if it does not contain sugar.
When sugar is eliminated from the diet, all foods start to taste better. Taste buds become more sensitive to the natural sweetness of foods. Soon, sugar cravings begin to dwindle and control over ones eating becomes easier and easier. Bodies start feeling better, calmer, and sleep improves.
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