PRECIPITATION OF DISORDERED DOLOMITE CATALYZED BY DISSOLVED SILICA AND IMPLICATIONS

This research investigated the effectiveness of electrocoagulation using iron and aluminium electrodes for treating cooling tower blowdown (CTB) waters containing dissolved silica (Si(OH)4), Ca2 + and Mg2 + . The removal of each target species was measured as a function of the coagulant dose in simulated CTB waters with initial pH values of 5, 7, and 9. Experiments were also performed to investigate the effect of antiscaling compounds and coagulation aids on hardness ion removal. Both iron and aluminum electrodes were effective at removing dissolved silica. For coagulant doses ≤3 mM, silica removal was a linear function of the coagulant dose, with 0.4 to 0.5 moles of silica removed per mole of iron or aluminium. Iron electrodes were only 30% as effective at removing Ca2 + and Mg2 + as compared to silica. There was no measurable removal of hardness ions by aluminium electrodes in the absence of organic additives. Phosphonate based antiscaling compounds were uniformly effective at increasing the removal of Ca2 + and Mg2 + by both iron and aluminium electrodes. Cationic and amphoteric polymers used as coagulation aids were also effective at increasing hardness ion removal.

Download Full-text

Removal of Dissolved Silica from Alkali Carbonate Brines

Industrial & Engineering Chemistry ◽

10.1021/ie50413a014 ◽

1944 ◽

Vol 36 (5) ◽

pp. 420-422

Author(s):

E. Gerald Meyer ◽

Charles E. McCarthy

Keyword(s):

Dissolved Silica ◽

Alkali Carbonate

Download Full-text

Alteration of Natural Uranyl Oxide Hydrates in Si-Rich Groundwaters: Implications For Uranium Solubility

MRS Proceedings ◽

10.1557/proc-257-465 ◽

1991 ◽

Vol 257 ◽

Cited By ~ 6

Author(s):

R.J. Finch ◽

R.C. Ewing

Keyword(s):

Corrosion Products ◽

Dissolved Silica ◽

Uranyl Phosphates ◽

Uranyl Silicates ◽

Solid Phases ◽

And Control

ABSTRACTThe uranyl oxide hydrates are common initial corrosion products of uraninite (nominally U02+x) during weathering. In the presence of dissolved silica these early-formed phases alter to uranyl silicates (most commonly soddyite, U2SiO8-2H2O, and uranophane, CaU2Si2O11·6H2O). Uraninite, however, usually contains radiogenic Pb, and the earlyformed Pb-poor uranyl oxide hydrates alter incongruously to uranyl silicates plus Pb-enriched uranyl oxide hydrates such as curite. Similar to dissolved silica, radiogenic Pb may also serve to limit the mobility of U in nature by fixing U in solid phases. Curite may also play an important role in the formation of uranyl phosphates, which are significantly less soluble than the uranyl silicates, and control U solubility in many groundwaters associated with altered U ore.

Download Full-text

Silicon isotopic chemistry in the C hangjiang E stuary and coastal regions: Impacts of physical and biogeochemical processes on the transport of riverine dissolved silica

Journal of Geophysical Research Oceans ◽

10.1002/2015jc011050 ◽

2015 ◽

Vol 120 (10) ◽

pp. 6943-6957 ◽

Cited By ~ 12

Author(s):

A. Y. Zhang ◽

J. Zhang ◽

J. Hu ◽

R. F. Zhang ◽

G. S. Zhang

Keyword(s):

Biogeochemical Processes ◽

Coastal Regions ◽

Dissolved Silica

Download Full-text

A model of Fe3+-kaolinite, Al3+-goethite, Al3+-hematite equilibria in laterites

Clay Minerals ◽

10.1180/claymin.1989.024.1.01 ◽

1989 ◽

Vol 24 (1) ◽

pp. 1-21 ◽

Cited By ~ 37

Author(s):

F. Trolard ◽

Y. Tardy

Keyword(s):

Stability Field ◽

Equilibrium Conditions ◽

Dissolved Silica ◽

Silica Activity ◽

Proposed Model ◽

Coexisting Phases ◽

Activity Temperature ◽

The Stability ◽

Fe Substitution ◽

Mineral Constituents

AbstractThe distribution of Fe3+-kaolinite, Al-goethite and Al-hematite and their contents of Fe and Al in bauxites and ferricretes are controlled by water activity, dissolved silica activity, temperature and particle size. The proposed model, based on ideal solid-solution equilibria in the Fe2O3-Al2O3-SiO2-H2O system, takes into account water and silica activities. By using the same considerations as those previously developed for the Fe2O3-Al2O3-H2O system, the model calculates the amounts of coexisting phases, Al or Fe substitution ratios in goethite, hematite or kaolinite, and the stability field distributions of the minerals under various conditions. Thermodynamic equilibrium conditions and element distributions within the mineral constituents are shown to be dependent on the parameters cited above. The model yields results compatible with natural observations on lateritic profiles.

Download Full-text