Precipitation Of Goethite Research Articles

Iron oxide deposits oh the roots ofphragmites australisrelated to the iron bound to carbonates in the soil

Abstract Iron plague was observed on the roots of Phragmites australis (the common reed) collected at six sites in southern Ontario and Québec, Canada. Sites were chosen along a wet‐dry gradient. The accumulation of iron oxides on the roots was site‐dependent but also varied between plants and microsites. Sequential extraction of iron from soil/sediment showed that the iron plaque is highly correlated (p<0.001) with the iron bound to carbonates of the substrate. It is hypothesized that the oxidation of siderite (FeCO3) in the rhizosphere results in the precipitation of goethite on the roots.

Oxygen Reactor for the Goethite-Zinc Leach Residue Process

In the goethite process for the recovery of zinc from neutral leach residue, iron in the hot acid leach solution is removed by an oxidation-hydrolysis step. Results are presented of an in-plant pilot test using oxygen, instead of air, in a new type of gas-liquid reactor. Under flow conditions providing residence times comparable to plant operations, ferrous iron oxidation and goethite precipitation were achieved in one reactor which were equivalent to that attained in three of the plant’s tanks. Goethite precipitate formed during the program was found to filter as good as conventional plant product and to contain less zinc and copper.

A mössbauer study of the iron mineralogy of acid-leached bauxite

The removal of iron from bauxite via some form of leaching step is particularly desirable because of the greatly enhanced value of low-iron bauxite in the refractory, abrasives and chemical industries, Previous investigations have shown that the iron minerals in Weipa bauxite are selectively dissolved under certain conditions, but that the extent of iron removal is limited unless total extraction of other mineral components takes place. In an effort to understand this behaviour, Mössbauer effect measurements have been made on samples of Weipa bauxite both before and after leaching with hydrochloric acid. Because of the finely divided state of the goethite present it has been necessary to take measurements at both 300 K and 4.2 K in order to fully characterize the iron mineralogy of the bauxites. Prior to leaching, the majority of the iron is present as hematite, which may be aluminium substituted by up to about 10%. Smaller quantities of aluminous goethite (usually about 15% substituted) and iron present within the structure of kaolin associated with the bauxite have also been found. About 95% of the hematite is removed during leaching, together with some of the gibbsite and boehmite present. A significant precipitation of goethite, containing a variable amount of aluminium, takes place during the leaching. From the limited number of samples investigated it appears that at higher acid concentrations the degree of alumiuium substitution of the precipitated goethite may decrease. Other studies of the forms of iron precipitated in aciiic chloride media have shown β-FeOOH (akaganéite) to be the principal product. It is believed that the finely divided goethite initially present in the bauxite has nucleated the precipitation thus leading to the formation of goethite rather than akaganéite.

Geochemical Model for the Origin of Precambrian Banded Iron Formations

Banded iron formations could have formed in shallow-water marine conditions from iron transported to the oceans in detrital sediments and silica transported in solution. If atmospheric P o 2 were significantly lower than at present and biological productivity were comparable to present-day values, the entire oceans below the thermocline would be anaerobic ( f o 2 ∼10 −70 ), while the surface mixed zone would be relatively oxidizing. The supply of Fe 2+ to the oceans in sediments is much greater than the supply of dissolved sulfate. Under anaerobic conditions, all the sulfur would be precipitated as pyrite, and Fe 2+ would build up in solution until siderite saturation was achieved (∼10 ppm Fe 2+ ). When the anaerobic deep water welled up onto a shallow platform, the dissolved Fe 2+ would be oxidized to goethite, and slight evaporation would cause precipitation of amorphous silica or magadiite. Siderite would be formed where the supply of organic carbon was sufficient to maintain anaerobic conditions at the sediment-water interface. Silica-secreting organisms are assumed to have been absent, and an oceanic pH value of 7.7 or lower (perhaps caused by a slightly higher atmospheric P co 2 would be required to prevent sepiolite precipitation. Quantitative calculations show that hydrogen ion released by oxidation of Fe 2+ and precipitation of goethite would be sufficient to prevent precipitation of calcite when the water is evaporated sufficiently to deposit a weight of SiO 2 equal to the weight of Fe 2 O 3 precipitated by oxidation of Fe 2+ . The predicted physical environment of deposition is similar to that of present-day shallow-water carbonates. This is in good agreement with sedimentological studies. Apart from the direct consequences of lowered atmospheric Po 2 , slightly increased Pcoa and the absence of silica-secreting organisms, the chemistry and thermal structure of the ocean 2 b.y. ago could have been identical to those of the present-day ocean.