Common salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in its natural form as a crystalline mineral is known as rock salt or halite. Salt is present in vast quantities in seawater, where it is the main mineral constituent. The open ocean has about 35 grams of solids per litre, a salinity of 3.5%.
Salt is the only mineral that humans eat, it's the only dietary mineral that's really a mineral. Since be begging of time animals and humans alike have sought it out.
Where does it all come from?
The sea takes in dissolved matter from two sources: rivers and volcanic activity on the seafloor. The rivers mainly provide ions from the weathering of rocks. The major ions are various silicates, various carbonates, and the alkali metals sodium, calcium and potassium.
Seafloor volcanoes mainly provide hydrogen and chloride ions. All these mix and match: sea organisms build shells from calcium carbonate and silica, clay minerals take up potassium, and the hydrogen is taken up in lots of different places.
Once all these processes have taken place, sodium ion from rivers and chloride ion from volcanoes are the two survivors. Water loves these two ions and can hold large amounts of them in solution. But sodium and chloride form an association and drop out of the water when they become concentrated enough.
They precipitate as solid salt, sodium chloride, the mineral halite.
When we taste salt, our tongues instantly dissolve it into sodium and chloride ions again.
The production process here at Port Hedland begins with seawater from the Indian Ocean. Powerful pumps with a total capacity of 1640 cubic metres per minute transfer the seawater into a nine-pond concentration system. Salinity is increased through each step of the system, which spans 7,800 hectares. Gravity causes the seawater to flow through the initial concentration ponds after which transfer pumps life the brine to flow into the final concentration pond. The saturation of the original seawater has increased from 17 to 90 per cent.
Axial flow pumps elevate brine from the concentration system along a specially designed 21 kilometre ditch system, which flows into a Pickle Pond. The solution is held in the Pickle Pond until it reaches full saturation and becomes feed stock for the crystallisers. The crystalliser system consists of 30 crystallisers with a combined area of 1,126 hectares. Saturated brine is pumped from the Pickle Pond via an open ditch to the crystallisers. Each crystalliser is filled with feed brine to a depth of 50 centimetres. The crystallisers are sampled each week to determine salt growth and the quality of brine. When the salt has grown to a thickness of 25 to 40 centimetres, the residual brine is drained off in preparation for harvesting.
Harvesting begins with the ripping of the salt, which has been grown on a salt pavement. The combination of salt and floor support the large trucks and equipment used in the harvesting process. The harvesting capacity is 1,800 wet tonnes per hour. Once harvesting is complete, the salt floor of the pond is levelled in preparation for the next batch of salt. Fresh brine is introduced into the crystalliser and process starts again.
The salt is transported to the wash plant by 180 tonne, bottom dump trucks, discharged into the hoppers and conveyed to twin-screw washers. The salt is washed to remove insoluble materials and fed onto a static screen where brine and seawater sprays remove the residual liquor that surrounds the salt crystals. The salt then flows onto a static screen where brine is removed. The salt washing process reduces a range of impurities including calcium, magnesium, sulphates and insoluble matter. The wash plant has a rated capacity of 1,500 tonnes per hour. The product salt is fed onto a radial stacker, which moves through an arc of 180 degrees to from a stockpile with storage capacity of over 750,000 tonnes.
The salt is left to drain for up to six weeks to reduce moisture and other impurities to meet the strict Dampier Salt quality standards. Once the salt has reached specification, it is transported by trucks, nine kilometres to the port stockpile area. The stockpiles are located near the Port Hedland deep-water berth.
The ship loader has a peak capacity of 3500 tonnes per hour and has the ability to load vessels of up to 75,000 DWT. *We have marked this point as a reference point, we quiet enjoy watching the salt being loaded, and there is a pull over area for cars to do this.
Please note GZ is the edge of a Salt pond owned by Rio Tinto, they have no problems with people observing the salt along the edges, touching the first few inches along the edge is fine. The road is dirt and is wide enough for a couple of cars to pull over safely.
To log this Earth Cache we require you to visit GZ and make some observations, consider the information given, then message us with the following answers to the best of your ability;
1. Looking out to the centre of the pond, how does it compare visually to the edge? Hypothesise about why this might be the case.
2. Looking at the edge closest to you how thick does the crust appear to be?
3. Considering your answers to Q1 & Q2 would you say this pond has been recently filled? Why or why not?
4.Describe the crystals and colours you can see in the crust, where do the colours come from?
5. Can you see any layering, why has layering occurred?
6. Can you see an footprints nearby, who made them and why are they here?
7. A photo of your team or GPS near the ponds upload as many photos as you like! (Optional)
You are welcome to log your answers straight away to keep your TB's and Stats in order but please message us with your answers within 1 week. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted without notice.
Source: Thoughtco, Wikipedia, Rio Tinto
