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Reading Selection, Lesson 15

Separating Solutions and the Salty Sea

A caravan of camels carrying salt

This caravan of camels is carrying salt across the Sahara Desert to be traded in another part of Africa.

Why is the sea salty? Where does all that salt come from? How does it get there? Much of the salt comes from the land. When it rains, rainwater dissolves soluble substances, including common salt (sodium chloride), from soil and rocks. Some of these substances eventually find their way into creeks and rivers, and from there, they are carried to the sea.
Why is the sea saltier than rivers? Once in the sea, soluble substances are concentrated. Heat from the sun evaporates the water from the sea but leaves the salts behind. Over millions of years, seas become saltier and saltier. For the same reason, lakes that have no outlet to the sea quickly become salty. Lakes can even be saltier than seas are.

Salt is a valuable commodity that has been traded for thousands of years. It is used in food, providing flavor and acting as a food preservative . It is also used to make a wide variety of chemicals. These chemicals are used in many industrial processes, including making glass, soap, and chlorine.

Men with wheelbarrows full of salt.

Salt making by evaporation, Salt Lake, Utah (early 20th century).

Today, most salt comes from mines, although a lot is also extracted from the sea or salty lake water. Salt has been extracted from salty bodies of water throughout history. One common method of extraction is to let the heat from the sun completely evaporate seawater that is trapped in pools or small lagoons.

In some desert areas, water is very scarce. But many of these deserts are near seas (or salt lakes), and salt can be removed from seawater to get fresh water. This process is called desalination. Seawater that is desalinated is fresh enough to drink and to grow crops. In some desalination plants, the saltwater is heated. The water evaporates away from the salt, as steam. The steam then condenses to form fresh water. This process requires a lot of energy, so it is very expensive. Other desalination plants remove salt from water by a process called reverse osmosis.

The Yuma desalination plant as seen from above

The Yuma desalination plant in Arizona is the world's largest desalination plant, capable of producing 72 million gallons of desalted water per day.

Questions

1. Use library or Internet resources to find information on the locations of the Salton and Aral Seas. Answer the following questions: What do the Salton and Aral Seas have in common? What environmental problems do they have?

2. It is widely believed that the term "salary" was derived from the Latin word for salt. Based on what you read in this article, why might this be true?

 

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