Fluoride can be removed from wastewater by addition of calcite. However, fluoride is often found in complex mixtures where other contaminants can affect the removal process. Batch experiments were used to determine the impact of phosphate (PO4 3 ) on the removal of fluoride from solution by calcite. In the experiments, up to 2,000 mg/L F and 500 mg/L PO4 3 were used with 150 mm and 1.18 mm calc...

Holocene biotic and abiotic marine calcite have a similar range of Mg contents (0 to 22 and 4 to 2 1 mol% MgC03, respectively), yet biotic calcite has Sr*+ concentrations that are consistently 1250 ppm higher than those of abiotic calcite. As in laboratory experiments, a positive linear relation is observed between Dsr and calcite Mg content. This produces two distinct linear trends on a plot o...

The calcite saturation status of soil-water systems in semiarid regions was reexantined taking into consideration organic ligand alkalinity and Ca-organic complexation. These factors have been forwarded as the reason for earlier reports of calcite Supersaturation in soilwater systems. We examined groundwaters beneath irrigated lands, soil-water suspensions in the laboratory using four soils and...

Soils often show supersaturation with respect to calcite. This study was undertaken to test alternative methods of measuring Ca2+ and COjactivities to assess their effects on measured ion-activity products (IAP) of calcite in soils. Soils were reacted with atmospheric CO,(g) and distilled H 2 0 for 1,3, and 7 d. The soil extracts were analyzed for pH, electrical conductivity (EC), cations, anio...

In the field of microbial biomineralization, much of the scientific attention is focused on processes carried out by prokaryotes, in particular bacteria, even though fungi are also known to be involved in biogeochemical cycles in numerous ways. They are traditionally recognized as key players in organic matter recycling, as nutrient suppliers via mineral weathering, as well as large producers o...

Coccolithophore contributions to the global marine carbon cycle are regulated by the calcite content of their scales (coccoliths) and the relative cellular levels of photosynthesis and calcification rates. All three of these factors vary between coccolithophore species and with response to the growth environment. Here, water samples were collected in the northern basin of the South China Sea (S...

Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time are believed to have been caused by tectonically induced variations in the Mg/Ca ratio of seawater (molar Mg/Ca>2=“aragonite seas”, <2=“calcite seas”). Here, I assess the geological e...

It is widely accepted that Vikings used sun-compasses to derive true directions from the cast shadow of a gnomon. It has been hypothesized that when a cast shadow was not formed, Viking navigators relied on crude skylight polarimetry with the aid of dichroic or birefringent crystals, called "sunstones." We demonstrate here that a simple tool, that we call "shadow-stick," could have allowed orie...

this study investigates the influence of some chemical additives such as methanol, ethanol, sodium oleat, chloroform and sodium hexametaphosphate (shmp) on the dry fine grinding of calcite (x50= 33 µm) using a stirred media mill. the experiments were carried out by a batch operation, and the change in colour properties (ry, whiteness and yellowness) of calcite powder. the results showed that th...