Showing papers on "Goethite published in 1975"

Adsorption of carbon dioxide on goethite (α-FeOOH) surfaces, and its implications for anion adsorption

Abstract: Carbon dioxide is strongly adsorbed as CO2–3 on moist goethite surfaces, but as both CO2–3 and HCO–3 on dry surfaces. On the basis of a model of the surface, sites for the adsorption of the carbonate species are suggested where these ions would play a role in redistributing surface charge. A similar role is proposed for strongly adsorbed anions such as phosphate.

The crystallinity of minerals; a new variable in pedogenetic processes; a study of goethite and associated silicates in laterites

Abstract: The crystallinity of minerals in terms of crystallite size distribution and lattice perfection is quantified by means of statistical measures derived from X-ray line profiles (2 cr values). A low degree of crystallinity facilitates the non-stoichiometric incorporation of foreign elements in the crystal lattice. Crystallinity is affected by a number of factors and in natural profiles it may vary laterally as well as vertically. For instance, goethite in laterite deposits shows decreasing crystallinity with increasing depth. Serpen- tine type minerals, on the other hand, show the lowest crystallinity at the surface where the degree of weathering is the most advanced. The presence of silica in migrating solutions prevents crystal growth and results in a low degree of crystallinity of minerals such as goethite. This has been observed in natural profiles and has been confirmed by laboratory experiments on the synthesis of goethite and sodium-birnessite. The crystallinity of minerals affects their response to extractive procedures. It could also be an important parameter in soil science.

Chemistry of iron in soils. ferric hydrolysis products

Abstract: A method has been developed for dividing hydrolysed ferric species into unpolymerized, polymerized and precipitated species. The colour developed with 8-hydroxy-7-iodoquinoline-5-sulphonic acid measures the concentration of unploymerized species and centrifugation gives the precipitated species. Polymeric species are found by difference. The pH and polymeric species decreases, precipitate formation increases and unpolymerized species remain constant on aging a partially neutralized ferric solution. With increasing OH/Fe ratio at a given age, the pH, polymeric and precipitated species increase and the unpolymerized species decrease. The concentration of unpolymerized species was independent of the anion (NO3, ClO4 or Cl). Goethite, lepidocrocite and â-FeOOH were formed in the solutions under various conditions. The rate and amount of precipitate formation was dependent on the degree of anion penetration for the polycations and precipitates and the total anion concentration. The ferric hydroxy polycations had V= 0.286 and empirical compositions of [Fe(OH)x 3-x]n where 2.2 < x < 2.9.

Electron-microscopic and Mössbauer Spectroscopic Studies of Iron-Stained Kaolinite Minerals

Abstract: An electron-microscopic and Mossbauer spectroscopic study of a range of kaolinites has revealed three distinct types of iron contamination within these minerals: a) Ferric ion may substitute for aluminium and be evenly distributed throughout the lattice, b) Ferric ion may be present as a crystalline coating of goethite, as indicated by lattice-imaging studies, or c) as an amorphous coating. The distribution of the iron in the groups b and c is non-uniform and is highest at the flake surfaces. Ferrous ion, when detected, is thought to be evenly distributed throughout the lattice. The size of the contaminating goethite crystallites and the observed Mossbauer spectra of these samples suggest that such particles are super-paramagnetic. All kaolinites can be cleaned by acid treatment except those having iron substituting for Al3+.

Mineralogy and Chemistry of the Patapsco Formation, Maryland, Related to the Ground-Water Geochemistry and Flow System: A Contribution to the Origin of Red Beds

Abstract: Red and drab-colored sediments of the Patapsco Formation were studied to determine if color changes, clay mineralogy, and iron content of the sediments are related to the present ground-water geochemistry (Back and Barnes, 1965) and the present ground-water flow system (Mack, 1962) The red color of the sediments becomes darker in the direction of the ground-water flow, particularly in local discharge areas This color change is related to the amount and kind of iron oxides in the sediments Hematite and goethite coexist in most of the red and mottled samples; hematite is more abundant than goethite in red sediments but is rarely found in drab sediments Large amounts of amorphous or poorly ordered iron oxyhydroxides in these sediments indicate that much of the iron has been introduced by diagenetic processes Lower iron oxide values prevail toward the center of the outcrop belt, and higher values prevail in the recharge area Detrital kaolinite and illite are the most abundant clay minerals Vermiculite and mixed-layer illite-smectite are almost always found in red colored sediments and are probably products of post-depositional diagenesis The mineralogic and chemical variations correlate regionally with the observed ground-water flow pattern and with observed changes in Eh and dissolved iron content of the ground water These results suggest that fluctuations in the ground-water flow system in conjunction with Eh and pH conditions caused precipitation of iron hydroxides that, on aging, have crystallized as goethite and (or) hematite

Manufacture of gamma-iron(III) oxide

Abstract: Acicular gamma-iron(III) oxide is manufactured by reacting an iron(II) salt solution with an aqueous solution of an alkali metal hydroxide and oxidizing the resulting suspension of iron(II) hydroxide in three stages. In a first stage, at most from 0.1 to 4% by weight of the amount of iron(II) hydroxide originally present is oxidized in the course of from 0.1 to 4 hours, in a second stage from 10 to 25% by weight of the said original amount are oxidized in the course of from 1.5 to 6 hours and in a third stage the remaining amount is oxidized. After the oxidation, the goethite formed is reduced to magnetite and the latter is then oxidized to acicular gamma-iron(III) oxide.

Method of making goethite powder

Abstract: A method of making goethite powder in which a ferrous hydroxide suspension is stirred for about 3 hours in an inert atmosphere and then is oxidized to form goethite powder.

Process for digesting goethite-containing bauxites according to the Bayer technology

Abstract: OF THE DISCLOSURE PROCESS FOR DIGESTING GOETHITE-CONTAINING BAUXITES ACCORDING TO THE BAYER TECHNOLOGY The invention relates to a process for the production of alumina according to the Bayer technology, of bauxites containing goethite and especially of boehmitic or diasporic bauxites, further for the acceleration of the digestion process, for the transformation of goethite into hematite, for the increase of the alumina yield and for the reduction of the caustic soda losses, the essence of which consists in that the digestion is carried out in the presence of 0.2-2.0 % Mg++ and/or Fe++ and/or Mn++ and/or Co++ ions reckoned upon the weight of the dry bauxite or of compounds and/or ores containing these ions in the indicated quantity. The process can be advantageously used simultaneously with the CaO-addition, also with digesting liquor containing NaCl and/or Na2SO4. The above mentioned bivalent ions are catalyzing the solubility of aluminium minerals and the transformation of goethite into hematite, the minimum required temperature of which can be reduced to 230 °C and for the transformation even 20 minutes at 240 °C and 2 minutes at 260°C are sufficient. The process can be highly advantageously used in the tube digesting equipment. The above enumerated bivalent cations reduce by further 10 % the losses of Na2O bound to the red mud, as compared with the technology applying CaO + Na2SO4-addition considered as optimum until now and increase by about 15 % the filtering capacity of red mud.

Chemistry of Iron in Soils. Ferric Hydrolysis Products

Abstract: A method has been developed for dividing hydrolysed ferric species into unpolymerized, polymerized and precipitated species. The colour developed with 8-hydroxy-7-iodoquinoline-5-sulphonic acid measures the concentration of unploymerized species and centrifugation gives the precipitated species. Polymeric species are found by difference. The pH and polymeric species decreases, precipitate formation increases and unpolymerized species remain constant on aging a partially neutralized ferric solution. With increasing OH/Fe ratio at a given age, the pH, polymeric and precipitated species increase and the unpolymerized species decrease. The concentration of unpolymerized species was independent of the anion (NO3, Clod or Cl). Goethite, lepidocrocite and 8-FeOOH were formed in the solutions under various conditions. The rate and amount of precipitate formation was dependent on the degree of anion penetration for the polycations and precipitates and the total anion concentration. The ferric hydroxy polycations had V= 0.286 and empirical compositions of [Fe(OH),3-x], where 2.2 < x < 2.9.