Bauxite

Utilization of fly ash can reduces the solid waste disposal problem and minimization of pollution also. Conventional production of bricks usually utilizes clay and shale as the source material and requires high temperature (900-1000 °C) kiln firing which is energy intensive, adversely affect the landscape, and can release high level of waste materials. Utilization of fly ash for making lime activated bricks not only give the waste utilization but also save earth shale as well as energy consumption and CO2 emission. The present study deals with the utilization of fly ashes for making lime activated fly ash bricks and their different property characterization after a normal water curing method up to 21 days. The crushing strength was observed 2.02, 3.17 and 5.32 MPa for 7, 14 and 21 days curing respectively. On the other hand apparent porosity and water absorption was observed 52, 52 , 50 and 46, 47 and 43% for 7 , 14 and 21 days curing respectively. The SEM-EDAX analysis was observed the initial formation of CASH phase along with free silica particle. But increasing curing time many new phases were observed such as CSH, CAH etc which reduce free silica particles present inside the bricks, responsible for further increase in strength.

Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressions on a karst limestone surface, and their subsequent lateritic weathering. Rare earth elements (REE) become concentrated in the bauxite deposits due to crystallisation of authigenic REE-bearing minerals, accumulation of residual phases and the adsorption of ions on clays and other mineral surfaces. REE are concentrated in the red mud waste generated by alumina production from bauxite through the Bayer process. Red muds thus contain on average 900 ppm REE compared with typical values of <100 ppm to ~500 ppm REE in the bauxites. Extraction of REE from red mud has been shown to be feasible although it is challenging due to the heterogeneous spatial distribution of REE in the bauxites and the need for development of appropriate processing methods. With annual European extraction of bauxite estimated to be approximately 3.5 million tonnes per annum, resulting in approximately 1.4 million tonnes of red mud from the production of alumina, understanding the REE resource potential of bauxites is integral to the assessment of European REE resources.

The Parnassus-Giona karst bauxite deposits contain significant concentrations of rare earth elements (400-500 ppm). Preliminary results from a pilot leaching study show that between 19 and 47% of rare earth elements in the bauxite are easily leachable using ion exchange agents such as ammonium sulphate.

During the Early Cretaceous, successive tectonic phases and several sea level fallsbrought up the exondation of the main part of Western Europe and the development of thick "lateritic" weathering. This long period of continental evolution ended with the UpperCretaceous transgressions. During this period, the exposed lands displayed a mosaic of diverse morphologies and weathered landscapes.The bauxitesare the most spectacular paleoweathering features, known for long insouthern France. Recently, new residual outcrops have been identified, trapped in the karsticdepressions of the Grands Causses. Other bauxitic formations, containing gibbsite, have alsobeen recognised coming with the Clay-with-Jurassic-cherts in the southeastern border of theParis Basin. These bauxitic formations overlay Jurassic limestone and are buried beneathUpper Cretaceous marine deposits. The recognition of bauxites up North to the southern ParisBasin significantly widens the extension of the Lower Cretaceous bauxitic paleolandscapes.On the Hercynian basementsoccur thick kaolinitic weathering mantles, which havebeen classically ascribed to the Tertiary. The first datings of thesein situpaleosoils, by meanof paleomagnetism and/or radiogenic isotopes, record especially Early Cretaceous ages. Thisis the case for the "Siderolithic" formations on the edges of the French Massif Central, butalso for the kaolinitic profiles on the Belgian Ardenne. In the Flanders, the Brabant basementis deeply kaolinised beneath the Upper Cretaceous cover. These paleosoils show polygeneticevolutions. The relief of these basement paleolandscapes may have been significant. Therewhere probably high scarps (often of tectonic origin) reaching 100 m in elevation or beyond,as well as wide surfaces with inselbergs, as in the present day landscapes of tropical Africaand South America.On the Jurassic limestone platformsare found diverse kaolinitic and ferruginousweathering products. Around the Paris Basin they show various facies, going from kaoliniticsaprolites to ferricretes. Due to the lack of sedimentary cover, the age of these ferruginous andkaolinitic weathering products has been debated for long, most often allocated to theSiderolithicsensu lato(Eocene-Oligocene). The recent datings, using paleomagnetism, havealso allowed to date them (Borne de Fer in eastern Paris Basin) back to the Early Cretaceous(130 ± 10 Ma). These wide limestone plateaus show karstified paleolandforms, such as vastclosed depressions with flat bottom broken by conic buttes, but also deep sinkholes in thehigher areas of the plateaus and piedmonts. The depth of the karst hollows may be indicativeof the range of relative paleoelevations. The dissolution features show few contemporaneous karst filling, thus implying that the karstland had not a thick weathering cover or that thiscover had been stripped off before or by the Late Cretaceous transgression. Nevertheless,some areas, especially above chert-bearing Jurassic limestone or marl, show weatheringproducts trapped in the karst features or as a thick weathering mantle.In the Paris Basin, the Wealden gutter looked like a wide floodplain in which fluvio-deltaic sands and clays deposited and on which paleosoils developed during time of non-deposition. The edges of the gutter were shaped as piedmonts linked up with the upstreambasement areas. The rivers flowing down to the plain deposited lobes of coarse fluvial sandsand conglomerates. The intensity of the weathering, the thickness of the profiles and theirmaturation are directly dependent on the duration of the emersion and the topographiclocation relative to the gutter. Near the axis of the gutter, where emersion was of limitedduration, the paleoweathering features are restricted to rubefaction and argillization of theLower Cretaceous marine formations. On the other hand, on the borders of the basin and onthe Hercynian basement, where emersion was of longer duration, the weathering profiles arethicker and more intensively weathered.The inventoryof the Lower Cretaceous paleoweathering features shows the complexityof the continental history of this period. Moreover, the preserved weathering products are onlya part of this long lasting period, all the aspects relative to erosion phases are still moredifficult to prove and to quantify. In this domain, the Apatite Fission TracksThermochronology (AFTT) can be helpfull to estimate the order of magnitude of thedenudation. Residual testimonies and subsequent transgressions may allow to estimaterelative elevations, but in return, we presently have not any reliable tool to estimate theabsolute paleoelevations. In the work presented here, the inventory allowed to draw acontinental paleogeographic map showing the nature of the weathering mantles and thepaleolandscape features, just as paleoenvironments and paleobathymetry presently appear onthe marine paleogeographic maps. For the future, the challenge is to make progress in datingthe paleoweathering profiles and especially in the resolution of these datings, in order tocorrelate precisely the continental records with the different events which trigger them(eustatism, climate, regional and global geodynamics). The final goal will be to build up astratigraphic scale of the "continental geodynamic and climatic events" facing the "sequentialstratigraphy" in the marine realm.

Red mud is highly alkaline (pH 13), saline and can contain elevated concentrations of several potentially toxic elements (e.g. Al, As, Mo and V). Release of up to 1 million m(3) of bauxite residue (red mud) suspension from the Ajka repository, western Hungary, caused large-scale contamination of downstream rivers and floodplains. There is now concern about the potential leaching of toxic metal(loid)s from the red mud as some have enhanced solubility at high pH. This study investigated the impact of red mud addition to three different Hungarian soils with respect to trace element solubility and soil geochemistry. The effectiveness of gypsum amendment for the rehabilitation of red mud-contaminated soils was also examined. Red mud addition to soils caused a pH increase, proportional to red mud addition, of up to 4 pH units (e.g. pH 7 → 11). Increasing red mud addition also led to significant increases in salinity, dissolved organic carbon and aqueous trace element concentrations. However, the response was highly soil specific and one of the soils tested buffered pH to around pH 8.5 even with the highest red mud loading tested (33 % w/w); experiments using this soil also had much lower aqueous Al, As and V concentrations. Gypsum addition to soil/red mud mixtures, even at relatively low concentrations (1 % w/w), was sufficient to buffer experimental pH to 7.5-8.5. This effect was attributed to the reaction of Ca(2+) supplied by the gypsum with OH(-) and carbonate from the red mud to precipitate calcite. The lowered pH enhanced trace element sorption and largely inhibited the release of Al, As and V. Mo concentrations, however, were largely unaffected by gypsum induced pH buffering due to the greater solubility of Mo (as molybdate) at circumneutral pH. Gypsum addition also leads to significantly higher porewater salinities, and column experiments demonstrated that this increase in total dissolved solids persisted even after 25 pore volume replacements. Gypsum addition could therefore provide a cheaper alternative to recovery (dig and dump) for the treatment of red mud-affected soils. The observed inhibition of trace metal release within red mud-affected soils was relatively insensitive to either the percentage of red mud or gypsum present, making the treatment easy to apply. However, there is risk that over-application of gypsum could lead to detrimental long-term increases in soil salinity.

The tailings dam breach at the Ajka alumina plant, western Hungary in 2010 introduced 1 million m3 of
red mud suspension into the surrounding area. Red mud (fine fraction bauxite residue) has a characteristically
alkaline pH and contains several potentially toxic elements, including arsenic. Aerobic and anaerobic
batch experiments were prepared using soils from near Ajka in order to investigate the effects of red
mud addition on soil biogeochemistry and arsenic mobility in soil–water experiments representative of
land affected by the red mud spill. XAS analysis showed that As was present in the red mud as As(V) in
the form of arsenate. The remobilisation of red mud associated arsenate was highly pH dependent and
the addition of phosphate to red mud suspensions greatly enhanced As release to solution. In aerobic
batch experiments, where red mud was mixed with soils, As release to solution was highly dependent
on pH. Carbonation of these alkaline solutions by dissolution of atmospheric CO2 reduced pH, which
resulted in a decrease of aqueous As concentrations over time. However, this did not result in complete
removal of aqueous As in any of the experiments. Carbonation did not occur in anaerobic experiments
and pH remained high. Aqueous As concentrations initially increased in all the anaerobic red mud
amended experiments, and then remained relatively constant as the systems became more reducing,
both XANES and HPLC–ICP-MS showed that no As reduction processes occurred and that only As(V)
species were present. These experiments show that there is the potential for increased As mobility in
soil–water systems affected by red mud addition under both aerobic and anaerobic conditions.

"Quantitative Thin Layer Chromatographic Study of Al3+ in Geological Samples

Mohamed Najar P.A.*, Sonali R.Gondane, Pravin G. Bhukte, Manoj T.Nimje and Suresh P. Puttewar

Analytical and Carbon & Waste Management Divisions
Jawaharlal Nehru Aluminium Research Development and Design Centre, Amravati Road, Nagpur – 440 023, India


SUMMARY

A facile and sensitive quantitative visual analytical method has been developed for the determination of Al3+ in geological samples. The alumina (Aluminium oxide; Al2O3) content in gibbsitic bauxite and related samples of geological origin was extracted in triple acidic medium. The sample solutions were purified and were subjected for quantitative thin layer chromatography (TLC) analysis. Combination of plain silica gel H and dilute aqueous solution of aluminon (0.005-0.50%) has been identified as the best chromatographic systems for the selective detection of Al3+.The important chromatographic parameters such as sample composition, pH effect, nature of adsorbent and mobile phase composition as well as detection limit were optimized in terms of spot size, colour stability and resolution of Al3+. The TLC chromatograms of Al3+ were quantitatively assessed scanning densitometry and digital image analysis. The Analytical potential of the optical quantitative methods have been verified for the quantitative TLC assessment of Al3+ in bauxite, soil, rock and aluminium spent potlining (SPL) samples with respect to the analogous wet analysis. Repeatability and reproducibility of the method were evaluated under the optimized experimental conditions.

Key Words: TLC, Geological samples, Al3+, Optical scanning densitometry, Digital image analysis
"

As an outcome of globalization and liberalization of economic policies, exploration for and mining of minerals have become one of the recent lucrative trades in India. Due to stringent environment legislations, reclamation and reforestation of the mined out sites have become obligatory. Information on distribution of nutrients before and after mining provides valuable insights while developing and executing the strategy for reclamation and revegetation of the mined out sites. Successful mine reclamation plan chiefly requires information on the soil characteristics in the area during its natural state. With this aim, investigations into spatial and temporal variations in soil nutrients and other physicochemical parameters among three proposed bauxite mine locations near Araku valley, India were conducted. Soil samples were collected every three months for two years. At each location, samples from three sites in triplicates from four successive layers (0 -5 cm, 5 -10 cm, 10 -15 cm and 15 -20 cm depth) were collected.