There are two distinct methods of producing concentrated ores known as ‘concentrates’, the dry or the wet method. The dry method involves the crushing of high-grade ore and removing waste material, leaving powdered ore with a low moisture content. During the crushing process, air is introduced into the powder with the result that, if the product becomes damp, this oxygen may react with the sulphur content of the ore to produce heat. In addition to this difficulty, oxygen ingress to cargo compartments stimulates self-heating of concentrates and ventilation should therefore be avoided, perhaps reducing oxidation still further by mechanically compressing the cargo and/or covering same with plastic sheeting. Furthermore, metallic elements present in such concentrates may emit explosive and/or toxic gases. Thus, extreme care should be exercised when entering a cargo compartment containing concentrates, bearing in mind that the compartment is likely to be short of oxygen. Even if dry, the dust of concentrates produced by the dry method may be toxic if inhaled or if allowed to touch skin. In the case of wet concentrates, the material consists of the sulphide portion of the ore separated from crushed rock by a water flotation process, and therefore containing water which may liquefy and shift dangerously across the cargo compartments due to moisture migration. It is thus vital that the moisture content of concentrate cargoes be analysed and checked prior to shipment and refused if this analysis reveals that the moisture content of the concentrate is too high. (It follows that, even if shipped dry, there is danger inherent in the practice of spraying water over concentrates at sea to cool the cargo). The IMO Code of Safe Practice for Solid Bulk Cargoes lays down that a certificate stating the relevant characteristics of the material to be loaded should be provided at the loading port, incorporating also the transportable moisture limit, and reference to IMO recommendations should be made in any charterparty or sale contract involving concentrates – eg:- “Carriage of concentrates to comply with IMO, local and international regulations and recommendations”. Large ships have been lost from failure to heed these recommendations.
- Bulk Iron Ore Concentrates Stowage Factor 11/20