Hydromagnesite

Secondary mineralization at Mount Keith produces hydromagnesite, while mineralization at Diavik includes carbonates of Mg, Ca and Na nesquehonite, calcite, vaterite, natrite, thermonatrite, natron, trona, gaylussite and northupite. The rate of carbon mineralization at the two mine sites was assessed using quantitative powder X-ray diffraction analysis and the Rietveld... 

Hydromagnesite is a basic magnesium carbonate 4MgC03.Mg(0H)2.4H20, while huntite is a mixed calcium magnesium carbonate SMgCOj.CaCOj. Both materials generally exhibit a platy crystal habit. 

This mixed product consists of small, platy particles with a relatively high surface area (15-20 m g ). The principal interest has to date been as a flame retardant Aller, principally for polypropylene. Both component phases decompose endothermically with the release of inert gas at relatively low temperatures. They are stable enough to allow incorporation into polymers such as polypropylene, but not polyamides. The performance of the two phases alone and in combination in polypropylene has been reported [91]. As expected from their thermal properties, hydromagnesite was the more effective flame retardant. The decomposition pathway of hydromagnesite has been shown to be considerably affected by pressure and this may affect its flame retardancy [71]. 

Synthetic basic magnesium carbonate is produced for filler purposes. This material has a composition that approximates to the formula TMgCOj. Mg(0H)24H20 and is essentially a synthetic form of the mineral hydromagnesite described earUer. It is mostly used as a smoke suppressant in PVC and similar polymers. It is reported in the trade Hterature as starting to decompose at about 200 °C. 

Walter, M. R., Golubic, S-, and Preiss, W. V. Recent stromatolites from hydromagnesite and aragonite depositing lakes near the Coorong Lagoon, South Australia. J. Sed. Petrol. 43, 1021-1030 (1.973). 

The evaporatively concentrated Mars water (Soln. 5.3B) was then allowed to drop in C02(g) concentration from 2 atm (the assumed initial Mars concentration) to 5.3 x 10-3 atm (the current average Mars concentration, Kieffer et al. 1992). This loss of CO2 leads to a significant increase in pH from 6.84 to 8.03 and a significant additional precipitation of hydromagnesite note the large drops in magnesium and alkalinity concentrations (cf. Soln. B and Soln. C, Table 5.3). 

Earlier, we examined the movement of salts through a Martian regolith under a freezing regime (Fig. 5.18). Initially, each layer (0.5km) was separately equilibrated this initial step removed virtually all the Fe(II) as siderite, most of the Ca as calcite, and a lesser percent of Mg as hydromagnesite. In a second step, we froze the system from the top down, which led to salt exclusion, increasing salt concentrations with depth, and additional precipitation of calcite and hydromagnesite (Fig. 5.18). 

CaCl2-6H20(cr) (antarcticite) 128.12 3MgC03-Mg(0H)2-3H20(cr) (hydromagnesite) 169.13... 

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