Salt from Seawater

About 200 Mt of sodium chloride are consumed every year in the world.

Some sodium chloride will be added to food, some will be used as a highway de-icing agent in cold climates, but most of it will be used in industries such as leather tanning, dye manufacturing, paper production, and in the production of other chemicals such as sodium carbonate, sodium hydroxide and chlorine.

The largest source of sodium chloride is the world's oceans.

So, how hard can it be to produce sodium chloride?

Surely you just evaporate the water off seawater and "hey presto", sodium chloride!

In reality, it's not quite that simple .....

Learn more in the September 2016 edition of AUS-e-NEWS.

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Hidden Salt in Food

Researchers at VicHealth and Deakin University compared how much salt people thought they consumed with how much salt they really had consumed and found that Australians were not only eating too much salt, but were also eating more salt than they thought they were!

Australians were found to be consuming between 8 and 10 grams of salt per day, about twice the amount recommended by the World Health Organisation (WHO) that recommends adults should eat less than 5 g of salt (a bit less than a teaspoon) per day. The "salt" they are referring to is "table salt" which has the chemical name "sodium chloride" and the chemical formula NaCl. Sodium chloride is actually an ionic substance made up of sodium ions (Na⁺) and chloride ions (Cl^-) in a ratio of 1:1 and it is the sodium ions (Na⁺) that are the cause for concern because elevated levels of sodium ions increase a person's risk of high blood pressure, heart disease and stroke. Unfortunately, non-Chemists often refer to this as elevated "sodium" levels rather than as elevated "sodium ion" levels.

If you want to reduce your sodium chloride intake, the first thing you can do is NOT add "table salt" to your food when you eat it. However, only about 20% w/w of our daily intake of sodium ions comes from adding sodium chloride to our food at the table before we eat it. The other 80%  w/w of the sodium ions we consume is already present in our food, either naturally or because it has been added during processing.

Natural sources of sodium ions in our food include:

• milk and cream: 50 mg of sodium ions per 100 g
• eggs: 80 mg of sodium ions per 100 g
• carrot: 69 mg of sodium ions per 100 g
• spinach: 79 mg of sodium ions per 100 g
• green beans, potatoes: 6 mg of sodium ions per 100 g
• pumpkin: 1 mg sodium ions per 100 g
• apple, banana, pear: 1 mg sodium ions per 100 g

By far the greatest source of sodium ions in our diet comes from eating processed foods:

• 1 slice of white bread (30 g) can contain 140 mg Na⁺
• 1 slice of cheddar cheese (20 g) can contain 140 mg Na⁺
• 1 foil pack of butter (7 g) can have 55 mg of Na⁺
• 1 small bowl of breakfast cereal (30 g) can have 140 mg of Na⁺
• 1 small packet of potato chips (45 g) can have about 300 mg of Na⁺
• 1 can (12 fl oz, about 350 mL) diet coke has 40 mg of Na⁺
• tap water contains about 20 mg Na⁺ per 1 L

Food you buy in packets from a supermarket will have a list of ingredients and you can read this to find the amount of sodium ions (Na⁺) present in the food.

However, there are many foods we buy that do not come in a packet which tells us how much sodium ion is present. These foods make up our "hidden salt intake". You may find this information on company websites, such as

• 1 McDonalds Big Mac contains 859 mg of Na⁺
• 6 KFC chicken nuggets with sauce has 1040 mg of Na⁺
• 1 slice (¹/₈ ^th) of medium pan Pizza Hut Meat Lover's pizza has 740 mg of Na⁺
• 1 Taco Bell black bean burrito contains 1030 mg of Na⁺

Many people forget that sodium ions are also present in many medicines. Effervescent medicines contain sodium hydrogen carbonate (or sodium bicarbonate) which helps them dissolve in water.
For example,:

• 1 effervescent Berocca tablet contains about 280 mg of Na⁺ while the film-coated Berocca tablet contains only 1.85 mg of Na⁺
• 1 Gaviscon Advance tablet contains 55 mg Na⁺ but 10 mL of liquid Gaviscon contains 141 mg of Na⁺
• 1 Panadol Actifast caplet contains 173 mg Na⁺ but 1 Panadol soluble tablet contains 428 mg of Na⁺

So, if you want a diet that's low in sodium, eat lots of fresh fruit and vegetables, drink lots of water, and avoid packaged food and "fast food", and, remember to choose "low sodium" medicines.

Reference:
http://www.abc.net.au/news/2016-03-24/reducing-salt-intake-could-save-thousands-of-lives-each-year/7274140

Further Reading:
Mass Conversions
Percent by Mass

Suggested Study Questions:

1. Convert the following masses in grams to masses in milligrams:
   • 5 g
   • 8 g
   • 10 g
   • 30 g
   • 100 g
2. Convert the following masses in milligrams to masses in grams:
• 1.85 mg
• 55 mg
• 69 mg
• 173 mg
• 859 mg
• 1040 mg
3. Calculate the percentage of sodium ions and the percentage of chloride ions in sodium chloride.
4. Use the information in the article to calculate the mass of sodium ions each adult Australian currently consumes as a result of :
   • adding table salt to food before eating it
   • table salt that is naturally present or is added to food during preparation
5. 100 g of milk contains 50 mg of Na⁺ . What is the percentage by mass of sodium in the milk?
6. One 30 g slice  of white bread contains 140 mg Na⁺. What is the percentage by mass of sodium in white bread?
7. For lunch, a student ate a sandwich made up of 2 slices of white bread, 2 foil packs of butter and a slice of cheddar cheese. She also ate a 200 g banana, and washed it all down with 250 mL of plain, unflavoured milk.
   • Calculate the mass of sodium ions the student consumed for lunch.
   • Calculate her consumption of sodium ions as a percentage of the WHO recommended daily intake of sodium ions.
8. A different student consumed a Big Mac, 1 can of diet coke, and a 200 g packet of potato chips.
• Calculate the mass of sodium ions the student consumed for lunch.
• Calculate her consumption of sodium ions as a percentage of the WHO recommended daily intake of sodium ions.
9. For her birthday, a Chemistry Teacher's class gave her a 500 g block of dairy milk chocolate. The label included the information that the block of chocolate contained 82 mg of sodium per 100 g.
   • What is the mass of sodium ions in the block of chocolate?
   • If each person in the class of 22 received an equal share of the block chocolate, what mass of sodium ions would each person consume?
10. In Australia, the maximum recommended dose of paracetamol (the active ingredient in panadol tablets) is 4000 mg per day. 1 soluble Panadol tablet contains 500 mg of paracetamol.
    • What is the maximum number of soluble Panadol tablets per day that an adult Australian should consume?
    • If an adult Australian consumed the maximum recommended dose of soluble panadol tablets in 1 day, what mass of sodium ions would they have consumed?
    • What percentage of the WHO recommended maximum intake of sodium would this amount of panadol be?

CGS and the Solvay Process

Coal seam gas (CSG) is any naturally occurring gas, such as methane, that is trapped in underground coal seams by water and pressure. Methane, often called natural gas, is a commercially valuable resource, so mining companies drill into the coal seam, pump the water out, which releases the pressure and forces the gases to the surface. Queensland is believed to have about 98% of Australia's coal seam gas reserve. More than 4,000 CSG wells in Queensland account for about 17% of that state's electricity. NSW has about 500 CSG wells.

The water that is produced in coal seam gas mining is not suitable for human consumption. The water is most often very salty and can contain heavy metals and toxic compounds.
A new drilling project in the Pilliga Forest in the north-west of NSW is expected to produce an average of 3 tonnes of salt a day over three years!

(http://www.smh.com.au/environment/coal-seam-gas-industry-faces-salt-overload-20131204-2yqx8.html#ixzz2mYw2aSQc)

That's a lot of salt! Left to itself, lying around near the mine, it will poison land and waterways. So what can you do with all this salt?

Salt, sodium chloride, is an important commercial chemical. It is used to produce chlorine and sodium hydroxide, and is used in other industrial process, it is used directly for snow and ice control, as a mineral in animal diets, as a preservative, as a flavouring agent, and as a reagent for water softening. The total (deliberate) production of sodium chloride world-wide is about 250 million tonnes per year.

One way to get rid of the salt produced in coal seam gas mining is to turn it into something else, sodium carbonate for instance.
In Australia, the Penrice Soda Products company in Osborne, South Australia, operates a plant using the Solvay Process to turn sodium chloride into sodium carbonate.
The overall chemical equation for the Solvay Process is
CaCO₃(s)   +   2NaCl (aq)      Na₂CO₃(aq)   +   CaCl₂(aq)
 CaCO₃(s) is present in limestone and the NaCl is the by-product of the CGS mining.
The company currently produces about 325,000 tonnes of sodium carbonate every year.

Further Reading:
density
yield

Solvay Process

Suggested Study Questions:

1. How much NaCl will the Pilliga Forest mining project produce in one year?
2. Assume that there are 4,500 CSG mines in Australia and they each produce 3 tonnes of salt a day. How much salt will be produced in one year in Australia from CSG mines?
3. The density of sodium chloride is about 2.2 g/cm³. Calculate the volume of salt produced each day by the Pilliga Forest CSG mine.
4. Assume a single truck can carry 100 tonnes of salt. How many truck loads of salt will be produced at the Pilliga Forest CSG mine each year?
5. Give one environmental issue that would be raised in trucking salt over large distances. Explain how the problem could be reduced.
6. Give one commercial problem associated with trucking salt over large distance using the same truck. Explain how the problem could be reduced.
7. What is the maximum amount, in tonnes, of sodium carbonate that could be produced using 1 truck load of sodium chloride?
8. What is the maximum amount, in tonnes, of calcium carbonate required to completely convert 1 tonne of sodium chloride to  sodium carbonate?
9. If the actual yield of sodium carbonate is 86.2%, what mass of sodium carbonate would be produced from the complete reaction of 1 tonne of sodium chloride?
10. Assuming the solvay process was used to convert all the salt from all Australia's CSG mines into sodium carbonate, how much sodium carbonate would be be produced?
11. World production of sodium carbonate is currently about 42 million tonnes per year. If Australia began production of sodium carbonate using all the salt produced in the CSG mines, what percentage increase would there be in world production of sodium carbonate?
12. What would you suggest Australia do with the salt produced as a by-product of coal seam gas mining?