An article in the journal Nature listed a series of data for the sole purpose of extracting sand and gravel faster than their natural recovery.
As the population increases, the use of sand continues to increase, and in the near future, the sand may erupt into a crisis even worse than the depletion of oil.
According to a United Nations statistic, an average of 50 billion tonnes of sand is mined globally every year, which, if gathered together, would be enough to build a wall around the equator with a height of 27 meters and a width of 27 meters.
However, an embarrassing fact is that the earth's sand resources are only 600 billion tons, and if no other solution can be found, then in more than 10 years, then mankind will face a situation where there is no sand available.
Because sand is very inconspicuous in daily life, it is widely used in construction, breeding and landscaping, smelting and glass.
In fact, sand is the second most used resource in the world, second only to water.
For a long time, it was thought that sand was an inexhaustible resource, like water, but in reality, the amount of sand available on Earth was very limited and its reserves were not very large. The reason for this is mainly related to the process of sand formation.
How is sand formed?
There are actually several types of sand, there are river sand, desert sand and sea sand, and one that people often use is river sand. The main component of river sand is silica, which is the most common and stable compound of silicon in nature.
In general, it takes tens of thousands to hundreds of thousands of years for river sand to form. River sand is actually a rock particle, which is the result of the joint shaping of various processes in nature, and the formation of river sand needs to go through several stages, which need to be completed by the power of nature and time.
First of all, the earth is a rocky planet, and the main part of the whole earth is all kinds of rocks, when the rocks are subjected to various natural forces, such as: wind, water and temperature changes and other factors.
So, when the rock is eroded by wind erosion and temperature changes, it will fall off the rock, and when the rock is located in the area where there are rivers, lakes and oceans, it will fall directly into the water.
The water washes over the surface of the rock and carries the fragments of the rock, and over time, these rock particles will rub and collide with each other under the action of water, and the rock will further break down into smaller particles.
In the process of river flow, when the speed of the water slows down or stops, the sand particles lose their momentum and accumulate on the riverbed or bank.
Some of this is carried downstream as the river is carried downstream, and the flow rate and volume of the river determine the ability of the river to carry sand, and generally large rivers can not only carry more river sand, but also carry larger grains of sand.
As the river flows, sand is piled up in the downstream riverbed as soon as the river slows down or encounters obstacles, forming sand beds and sandy beaches. Some of it continues to flow along the river and eventually into the sea, where it becomes sea sand.
Under the action of natural forces and the blessing of tens of thousands of years, those chemically unstable substances in the rock are gradually stripped away, leaving only silica with high hardness and relatively stable chemical properties, which is why river sand is silica.
There are many deserts on Earth, why is there not enough sand?
As explained above, the formation process of river sand is not easy, although in nature, river sand is not a non-renewable energy source, but it takes a long time to form.
At the current rate of human use, it is far from keeping up with the rate at which sand is formed, so it is at risk of depletion.
At this time, some people will say that there is no shortage of sand on the earth, there are vast deserts on the earth, and sand depletion is a false proposition.
In fact, the amount of sand in the desert, although large, is not the sand available to humans. The Sahara Desert, for example, covers an area of more than 9.32 million square kilometers, and the average sand thickness in the Sahara is 3.6 meters.
According to the density of sand, the weight of 1 cubic meter of sand is 1.3-1.6 tons, then it can be calculated that the weight of sand in the Sahara Desert is about 4000 trillion tons.
If the sand in the Sahara Desert could be used, it would be enough for humans to use it for millions of years, but the sand in the desert would not be usable at all.
This is because the sand in the desert has relatively small particles. For example, in the construction industry, which consumes a large amount of sand, sand is used as a fine aggregate in concrete, which is used to fill the gaps of coarse aggregate, and needs to withstand a certain amount of force.
Therefore, there are certain requirements for the size of the sand, and in the construction industry, it is stipulated that the diameter of the sand cannot be less than 1 mm, and below this diameter, then the force that the sand can withstand in the concrete is limited.
However, the sand in the desert is generally dust sand, which is generally less than 0.25 cm in diameter, which cannot meet the needs of the construction industry.
In addition, the structure of the sand in the desert is also relatively special, under the action of the wind, the particles rub and collide with each other, and they are all round or smooth particles. The sand required for buildings is mostly irregular in shape, which is conducive to the concrete to increase enough friction and increase the strength of the concrete. Whereas, the sand in the desert cannot provide enough friction due to its round, smooth particles.
In addition, the sand in the desert, because it has not been washed by rainwater, is rich in alkaline substances, and when the sand in the desert is used with other materials, a chemical reaction will occur, which not only reduces the strength of the building, but also affects its quality.
It is for this reason that the desert countries in the Middle East, although surrounded by sand, spend a huge amount of money every year to buy sand from outside.
In addition to the sand in the desert, there is also a kind of sand, that is, sea sand, due to the high salt content, even after desalination, it will corrode the steel bar, causing the concrete to be brittle, and the road surface can be repaired, but it cannot carry the beams to build the house.
Therefore, it creates an embarrassing situation, that is, only river sand can be used, and rivers only occupy a very small proportion of the global area, which leads to the very scarce amount of river sand and is a scarce resource.
Sand promotes the prosperity of the city
Pascal Pedouzi, a scientist at the United Nations Programme, said that the earth's prosperity is actually built on sand, but it has not received more attention than other natural resources, and people are looking to "copper, lithium, oil and gold, among others".
In fact, sand also plays a major role in the prosperity of mankind today, and the buildings of cities are built under the accumulation of sand.
Some scholars in Europe have calculated that it takes an average of 200 tons of sand to build a house, and 30,000 tons of sand to build a 1-kilometer highway. In Europe, the average European consumes about 6 tons of sand per person per year.
In recent years, due to China's rapid development, in the process of development, it also consumes a lot of sand, according to statistics, China consumes about 20 billion tons of sand every year, due to the lack of domestic sand resources, it also needs to import a large amount of sand from outside every year.
At present, due to the gradual depletion of sand resources, there is a serious shortage of sand in the global sand market, and the price has increased 11 times in 11 years, so the supply is still in short supply.
If it continues, then there will be no sand available. Fortunately, the current scientific and technological means of human beings can accelerate the formation process of river sand.
It is to use machines to make the sand that takes tens of thousands or hundreds of thousands of years to form without natural force, and directly use the machine to crush it to meet the standard of sand use.
In addition, some scientists are now studying the recycling of concrete, and those demolished houses are also rich in sand, and scientists are crushing and refining concrete to make it a recyclable natural resource.
#头条创作挑战赛#