Goethite process

The goethite process precipitates crystalline aFeO-OH (goethite) as well as PFeO-OH, aFe202, and amorphous phases. The reaction is carried out at 90°C and pH 3.0, for 4—6 h in either batch or continuous fashion, and the iron(III) ion must be kept <1 g/L. Both jarosite and goethite soHds are usually lagooned. 

In the goethite process, the precipitation of iron from solution occurs in the form of hydrated ferric oxide, FeOOH. The commercial development of the process was due to Societe de La Vielle Montagne. The process basically involves the reduction of iron to the ferrous state, and this is followed by oxidation by air at a temperature of around 90 °C and at a pH controlled at around 3.0. The reaction can chemically be shown as ... 

The principal differences between the goethite and the jarosite processes take place following the hot acid leaching of the zinc ferrite residues. In the goethite process, the liquor from hot acid leaching, holding (in g l-1) 100 Zn, 25-30 Fe3+ and 50-60 H2S04, is initially subjected to a reduction step, where the ferric iron is reduced to the ferrous form by reaction with unroasted zinc sulfide concentrate at 90 °C ... 

Figure 5.46 The Vielle Montagne goethite process. Figure 5.47 The hematite process.

Processes requiring sulphation require the use of aqueous or concentrated sulphuric acid. ..as the sulphating agent. In many cases the leach liquors produced are highly contaminated and recovery procedures play a vital part. Fortunately, it has recently become easier to remove dissolved iron using either the jarosite process or the goethite process. ... 

Goethite process. Precipitation of goethite, FeOOH, is performed by adding a solution of ferrous sulfate to zinc calcine along with oxygen or air to ensure the oxidation of ferrous iron at a pH of about 3. Ferrous sulfate comes from copperas (FeSO 7H2O) or from the leaching of zinc ore concentrates ... 

Hematite process. The leaching in the hematite process is the same as that used in the goethite process, but the precipitation of iron is conducted inside an autoclave at 180 to 200°C without neutrahzation ... 

Torfs, K.J. Vliegen, J. (1996) The Union Miniere goethite process plant practice and future prospects. Iron Control Disposal. In Dutrizac, J.E., Harris, G.B. (eds.) Proc. Int. Symp. Iron Control HydrometalL, 2nd ed., pp. 135-146. Canadian Institute of Mining, Metallurgy and Petroleum, Montreal, Quebec, Canada. 

The final product of all the above processes is iron(III) oxide, a-Fe202, but its properties are deterrnined by the method of preparation. Thermal dehydration of goethite yields a pigment of lowest (4.5 g/cm ) density. The highest (5.2 g/cm ) density pigment is one prepared by two-stage calcination. The particle si2e varies from 0.3 to 4 p.m the refractive index varies from 2.94 to 3.22. 

Fig. 8.31 Left) In the Mossbauer spectrum taken in the Columbia Hills at a rock called Clovis the mineral goethite (GT) (a-FeOOH) could be identified. GT is a clear mineralogical evidence for aqueous processes on Mars. Right) The rock Clovis is made out of rather soft material as indicated by the electric drill-current when drilling the - - I cm deep hole seen in the picture. Drill fines are of brownish color. The pattern to the right of the drill hole was made by bmshing the dust off the surface by using the RAT...

The alkali process uses sodium hydroxide and is well known as Bayer s process. It involves relatively simple inorganic and physical chemistry and the entire flowsheet can be divided into caustic digestion, clarification, precipitation and calcination. Although mineral assemblage in bauxites is extensive, processing conditions are primarily influenced by the relative proportions of alumina minerals (gibbsite and boehmite), the iron minerals (goethite and hematite), and the silica minerals (quartz and clays-usually as kaolinite). 

In the ultimate analysis it may be pointed that the aforesaid hydrolysis processes are no doubt technically very satisfactory and tolerable, but environmentally this is not the case. The different processes yield jarosite, goethite and hematite, all of which retain considerable amounts of other elements, especially, zinc and sulfur. The zinc originates mainly from undissolved zinc roast in the iron residues, and sulfur from sulfate, which is either embodied into the crystal lattice or adsorbed in the precipitate. As a consequence of the association of the impurities, none of these materials is suitable for iron making and therefore they must be disposed of by dumping. The extent of soluble impurities present in the iron residues means that environmentally safe disposal not an easy task, and increasing concern is being voiced about these problems. An alternative way of removing iron from... 

Violante A, Krishnamurti GSR, Pigna M (2008) Mobility of trace elements in soil environments. In Violante A, Huang PM and Gadd G (eds) Wiley-JUPAC series on biophysico-chemical processes of metals and metalloids in soil environments. John Wiley Sons, Hoboken, USA Waltham AC, Eick MJ (2002) Kinetic of arsenic adsorption on goethite in the presence of sorbed silicic acid. Soil Sci Soc Am J 66 818-825 Waychunas GA, Fuller CC, Rea BA, Davis J (1996) Wide angle X-ray scattering (WAXS) study of two-line ferrihydrite structure Effect of arsenate sorption and counterion variation and comparison with EXAFS results. Geochim Cos-mochim Acta 60 1765-1781... 

Goethite A process for removing iron from leach liquors from hydrometallurgical leaching operations. Used in recovering zinc from the residues of the electrolytic zinc process. See also Jarosite, Haematite. 

Jarosite [Named after the mineral, first recognized at Jarosa, Spain] A process for removing iron from the leach liquors from hydrometallurgical operations. First used in 1964 in processing zinc sulfate liquors at Asturiana de Zinc, Spain. Also used for recovering zinc from the residues from the electrolytic zinc process. See also Goethite, Haematite. 

The evolved hardpans (Fig. 1b) are composed by rhythmic alternation of submillimetric goethite-rich (ochreous) and hematite-rich (red) layers. This layering is the result of a complex evolution of the pristine authigenic Fe-oxides and -oxyhydroxides during which the mineral phases are cyclically involved in transformation processes including recrystallization, dissolution and reprecipitation (Carbone etal. 2005). 

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