Magnesium processing parameters

Slurry Viscosity. Viscosities of magnesium hydroxide slurries are determined by the Brookfield Viscometer in which viscosity is measured using various combinations of spindles and spindle speeds, or other common methods of viscometry. Viscosity decreases with increasing rate of shear. Fluids, such as magnesium hydroxide slurry, that exhibit this type of rheological behavior are termed pseudoplastic. The viscosities obtained can be correlated with product or process parameters. Details of viscosity deterrnination for slurries are well covered in the Hterature (85,86). 

Nonetheless, the general understanding of magnesium and calcium carbonation reactions has improved significantly (see also the studies by Hanchen et al. [107-110] on the relative importance of process parameters such as temperature, C02 pressure and particle size distribution). Studies involving a three-step process of olivine carbonation, involving (i) dissolution of olivine (ii) precipitation of magnesite and (iii) precipitation of silica in an aqueous solution, were recently reported from Norway [69], where the process proceeds without chemical additives at 10-15 MPa and 403-523 K. No reaction rates were reported, however. 

Chemical inhibitors, when added in small amounts, reduce corrosion by affecting cathodic and/or anodic processes. A wide variety of treatments may be used, including soluble hydroxides, chromates, phosphates, silicates, carbonates, zinc salts, molybdates, nitrates, and magnesium salts. The exact amount of inhibitor to be used, once again, depends on system parameters such as temperature, flow, water chemistry, and metal composition. For these reasons, experts in water treatment acknowledge that treatment should be fine tuned for a given system. 

All aspects of prevention of magnesium (and aluminium) dust explosions in storage, handling or processing operations are covered in two recent US National Fire Codes [1]. Effects of various parameters on ignition of magnesium powders were studied [2], Maximum explosion pressures of 7.9 bar, with maximum rate of rise of 884 bar/s have been recorded [3],... 

In conclusion, the incorporation of 50% magnesium stearate and talc before precompression and the other 50% before the final compression improves the compression behaviour. At the same time, it decreases the coefficients of variation of UPF the weight of the tablet and dissolution parameters. From these results, the process from experiment was chosen for the experimental designs. 

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