Category Chemistry

WHAT IS OPENCAST MINING?

Opencast mines are used when the deposit lies near the surface. Overlying earth and rock can be moved by machine or washed away with water. Although opencast mining is cheaper than digging deep mines, some people feel that the environmental costs of it are high, as large areas of land are laid bare and wildlife destroyed. Nowadays great attention is often paid to landscaping the area after an opencast mine has been abandoned. Many are made into parks or wildlife refuges. Planting the areas also helps to stabilize heaps of spoil.

Opencast mining operation involves generation of massive mine waste, altering the existing landscapes, alterations to drainage patterns etc. As a result, significant areas of land are degraded and existing ecosystems are replaced by undesirable wastes. To mitigate the impact on environment, a structured and adoptable environment management practice is being continuously developed at NLCIL. Eco-friendly mining can be broadly brought up under conservation of natural resources, prevention and regulation of polluting activities and action plans for eco regeneration.

Opencast mining operations involve huge quantities of overburden removal, dumping and backfilling in excavated areas. A substantial increase in the rate of accumulation of waste dumps in recent years has resulted in greater height of the dump for minimum ground cover area and also given rise to danger of dump failures. Further, steeper open-pit slopes are prone to failure. These failures lead to loss of valuable human life and damage to mining machinery. There is a need for continuous monitoring of dump and pit slopes, as well as for providing early warning before the occurrence of slope failure. Different technologies have been developed for slope monitoring. After studying the features and limitations of existing slope monitoring systems, it determined that there is a need to provide a reliable slope stability monitoring and prediction system by using a solar power-based long-range wireless sensor network for continuous monitoring of different prevailing parameters of slope stability. An accurate prediction of slope failure using a multiparameters-based prediction model is required for giving warning per the danger levels of impending slope stability. Considering the requirement, a slope failure monitoring and prediction system has been developed by the authors, using a wireless sensor network for the continuous monitoring of slope failure and to provide early warnings. The chapter describes details of slope stability mechanism, parameters affecting slope failure and triggering aspects, monitoring systems, prediction software, and laboratory experiments for calibrating geosensors and field installation of the developed system.

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CAN MINERALS BE OBTAINED FROM PLACES OTHER THAN THE EARTH’S CRUST?

For practical purposes, the Earth’s crust is the only source of minerals. There are, of course, huge amounts of minerals in the Earth’s core and in space, but at the moment it is not possible for us to reach and use them.

Hard rock minerals could be mined from an asteroid or a spent comet. Precious metals such as gold, silver, and platinum group metals could be transported back to Earth, while iron group metals and other common ones could be used for construction in space.

Difficulties include the high cost of spaceflight, unreliable identification of asteroids which are suitable for mining, and ore extraction challenges. Thus, terrestrial mining remains the only means of raw mineral acquisition used today. If space program funding, either public or private, dramatically increases, this situation may change as resources on Earth become increasingly scarce compared to demand and the full potentials of asteroid mining—and space exploration in general—are researched in greater detail.

Asteroid mining could shift from sci-fi dream to world-changing reality a lot faster than you think. Planetary Resources deployed its first spacecraft from the International Space Station last month, and the Washington-based asteroid-mining company aims to launch a series of increasingly ambitious and capable probes over the next few years.

The goal is to begin transforming asteroid water into rocket fuel within a decade, and eventually to harvest valuable and useful platinum-group metals from space rocks. “After that, I think it’s going to be how the market develops,” Lewicki told Space.com, referring to the timeline for going after asteroid metals.

“If there’s one thing that we’ve seen repeat throughout history, it’s, you tend to overpredict what’ll happen in the next year, but you tend to vastly underpredict what will happen in the next 10 years,” he added. “We’re moving very fast, and the world is changing very quickly around us, so I think those things will come to us sooner than we might think.”

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IS WATER USEFUL IN MINING?

In deep mines, water can pose a great danger, undermining layers of rock and causing collapses and flooding, but other types of mining use water to great advantage. Sulphur, for example, can be mined in an unusual process using water. Three pipes of different sizes, one inside another, are drilled into the sulphur reserves. Then extremely hot water, under pressure, is pumped down the outer pipe. This melts the sulphur. Compressed air is then pumped down the central pipe, causing the melted sulphur to move up the middle pipe to the surface. This system was developed by an American engineer, Herman Frasch (1851-1914).

Mining water use is water used for the extraction of minerals that may be in the form of solids, such as coal, iron, sand, and gravel; liquids, such as crude petroleum; and gases, such as natural gas. The category includes quarrying, milling of mined materials, injection of water for secondary oil recovery or for unconventional oil and gas recovery (such as hydraulic fracturing), and other operations associated with mining activities. Dewatering is not reported as a mining withdrawal unless the water was used beneficially, such as dampening roads for dust control.

During some mining activities, particularly gold mining and dredging, water is used for sluicing and flushing out minerals. In most mining operations the majority of this water is recycled, so water loss from rivers and streams is minimised. Water take (abstraction) can be more pronounced where dredging occurs near the riverbed. Loss of water may reduce in stream habitat, elevate water temperatures, and increase summer algal blooms, which may affect invertebrate and mahinga kai communities.

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Why do things take longer to cook at higher altitudes?

Mountaineers find it time-consuming and difficult to brew a good cup of tea or cook food, especially as they climb higher. You just can’t make your usual cup that cheers on the top of Mount Everest.

Water normally starts boiling when it reaches a temperature of 100  (or 212 ). But this is true only if you are at sea level. As you go higher, due to a fall in the atmospheric pressure, water starts boiling at a lower temperature. (70  or 158  on the summit of Mount Everest!)

This heat is not enough to extract the best flavour from the tea leaves. Cooking in a saucepan or pressure cooker also takes much longer on mountain tops.

 

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WHY DO WE COOK FOOD?

There are several reasons why food is cooked. Most obvious is the fact that cooking makes food hot! In cold weather, hot food is especially warming and comforting. Cooking also alters the flavour and texture of food. Heat causes chemical reactions to take place, altering the way that the food tastes and feels in our mouths. Because of these chemical reactions, cooking may also make food easier to digest. Finally, cooking can make food safer to eat by killing bacteria within it.

People cook food for many different reasons and while it is best to eat some foods raw such as fruits and vegetables, there are some advantages to cooking food. Food can be cooked for the following reasons:

  1. To change or improve the taste of the food e.g. flour being used to make cake. A cake tastes far more delicious than raw flour. Another example includes cooking sugar to make browning used to stew meats. The sugar is no longer sweet but its new taste is desirable when cooking beef etc.
  2. To change or enhance the appearance of the food e.g. using rice to make fried rice, preserving mango to make jam
  3. To change the texture (the way something feels) of food e.g. using cornmeal to make pastilles. Raw cornmeal is very grainy and coarse but when it is cooked with a liquid it becomes softer, smoother and more palatable.
  4.  To make food safer to consume (eat). A good example of this can be found in our where eggs are cooked to make devilled eggs. Raw meat, fish, poultry and egg should all be cooked to make them safe to consume since they contain bacteria that can be harmful to us. For instance, eating raw eggs can cause Salmonella poisoning whose symptoms include vomiting and diarhoea, nausea and general ill health.
  5.  To make foods more digestable e.g. tough cuts of meat, hard staples such as rice and cassava. Cooking these foods makes it easier for the body to use it and get all the nutrients from it.
  6. To increase the shelf life of the food e.g. making jam from guava. Adding sugar and heating the guava to make jam will make a product that has a longer shelf life than fresh guavas.

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HOW WERE WINDOWS MADE BEFORE GLASS WAS WIDELY AVAILABLE?

Windows have three main purposes: to let light into a building, to allow ventilation, and to allow the occupants to see out. Although glass has been made for thousands of years, it is only comparatively recently those techniques have been developed for making large sheets of glass for windows. Before that, although small sheets of glass were available, they were expensive. Small windows were sometimes covered with thin panels of horn. Although this could not be seen through, it did let in a certain amount of light and kept out cold winds.

While the modern window might seem like a pretty simple contraption, it’s actually made from dozens of carefully-engineered parts. Double-glazed windows are able to insulate far better than a single sheet of glass – but even that required hundreds of years of refinement and engineering before it could be made thick and flat enough to actually see through.

Glass, as a material, is rare in nature. Usually, it comes in the form of obsidian – which is entirely black. Synthetic glass first came to be widespread in ancient Egypt and Mesopotamia in around 3500 BCE, and came to be used for vases and cups thousands of years after that.

Glass windows, on the other hand, came much later. The ancient Romans used them, sporadically, in the more up-market villas and government buildings – though their optical qualities were far behind what we might expect today. In certain places, like churches, this difficulty became an opportunity: stained glass windows allowed for the depiction of certain religious scenes. In this setting, transparency didn’t matter.

The earliest forms of window glass were ‘broad sheet’. These were made by first blowing a tube of glass, and then cutting off one side and rolling the whole thing flat.

The difficulty of manufacturing glass windows made them something of a status symbol – and this continued right up to Tudor England, where only the wealthiest households could afford windows of a decent size. In Europe, the Italian renaissance left no aspect of culture or industry untouched. Windows there became taller and sleeker, and separated by mullions and transoms (the wooden crossbeams which run across the surface of a window). As time went by, these elements were made progressively narrower – so that more light could pass through the window.

The 17th century saw the introduction of an entirely different sort of window: the sash window. This variety of window consisted of two moving panels, which could slide behind one another to create an opening. Windows of this sort needed to be made from ‘crown glass’: a more affordable material created by spinning discs of the stuff, and then cutting those discs into broad sheets.

Today, our windows are almost universally made from machined ‘float’ glass. This process came about in the mid 19th century, and though it’s been extensively refined since then, the principles used today remain the same: the molten glass is poured into a bath of molten tin. The two materials are immiscible, meaning the sheet floats upon the molten tin as it cools (like oil might float on water). The result is a perfectly smooth sheet on both surfaces, which, after a little bit of extra treatment, becomes perfectly transparent.

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