Every tonne of water in a bauxite cargo is a tonne of freight paid for nothing. In sea transport, too much moisture can also become a safety issue. Moisture is one of the most practical numbers on any bauxite contract.
Two kinds of water
Bauxite contains water in two forms, and they are reported separately.
- Chemically bound water is part of the minerals themselves, especially gibbsite. It is measured as part of LOI and cannot be dried off at normal temperatures.
- Free moisture is water held on and between particles: rain, groundwater and spray water. It is measured by drying a sample at a moderate temperature and is what contracts usually mean by "moisture".
Why free moisture matters
Cost
Freight and handling are charged on wet tonnes, while chemistry is usually priced on dry tonnes. Higher moisture means more money spent moving water.
Handling
Wet, clay-rich fines become sticky. They can block chutes and hoppers, build up in trucks and conveyors, and make reclaiming stockpiles harder. Very dry ore, on the other hand, can be dusty.
Shipping safety
Some fine, moist bulk cargoes can lose stability at sea when the ship's motion lets water migrate through the cargo, creating a wet, mobile layer. The loss of the bulk carrier Bulk Jupiter in 2015 while carrying bauxite led the shipping industry to look closely at this risk for bauxite.
The International Maritime Solid Bulk Cargoes (IMSBC) Code governs bulk cargoes at sea, and it now treats bauxite fines that may be prone to this behaviour with specific testing and moisture requirements. In practice, shippers must provide accurate moisture data and, where the rules require, test results showing the cargo is safe to carry. The exact requirements depend on the cargo's particle size and properties, so they should be confirmed with the shipper, the master and the relevant authorities for each voyage.
How a mine keeps moisture in check
- Stockpile on drained ground, away from water flows.
- Build dry stocks before the monsoon, so wet-season shipments draw on ore mined in dry weather.
- Screen out excess fines where they hold the most water.
- Avoid over-spraying stockpiles during dust control.
- Measure moisture at loading, not only in the stockpile, so the declared figure reflects what is actually shipped. See bauxite sampling and quality control.
What to put in the contract
| Term | Why |
|---|---|
| Maximum free moisture | Caps freight paid on water |
| Basis for chemistry and price (dry or wet) | Avoids disputes over adjustments |
| Moisture sampling point and method | Makes results comparable |
| Shipping documentation for sea cargo | Ensures compliance with the IMSBC Code |
On the Konkan coast, the monsoon is the biggest moisture risk. Our article on bauxite logistics from Raigad covers seasonal planning.