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CH PTER

M TERI LS NDMETHODS

The present work attempts to trace the variation in the physical andchemical behaviour of ilmenite since its release from country rocks andsubsequent transportation to the coast through the progressiveweathering environments of laterite sedimentary rocks rivers andestuarine systems Since the hinterland of the study area consists ofcrystalline and sedimentary rocks and their weathered forms laterites ,the contribution of each lithological system to the beach placer isattempted. Though the main emphasis of the study is on thecharacterization and grading of the ore along the coast particularly inthe placer deposits such work as mentioned above would go a long wayin unraveling the genesis of the placers which have not been completelyresolved so far.

3.1 S MPLE COLLECTION NDPRE TRE TMENT

3.1.1 Sampling

Representative samples were collected from var ious environments ofmineral occurrence like primary rocks laterites rivers estuary andbeaches Fig. 3.1 . Rock samples up to 20 kg were crushed for possibleseparation of ilmenite and huge quant iti es of rock powder from thecrushing units were subjected to wet panning The collection of ilmenitewas attempted from crystalline rock samples but the mineral gra inswere always found associated with minerals like pyroboles rendering thephysical separation of ilmenite grains difficult. Laterites and sand stonesamples were collected from road cut tings and quarries and crushed atthe location itself before insitu panning The alluvial samples were

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akshadweep

o9

o830

20 Kilometers0

N

o

Sample locationBeachEstuary

:0 RiverTeriSedimentary RockLaterite SubsurfaceCrystalline rock sampleKhondaliteGarnet biotite gneiss with MigmatiteCharnockiteTertiary SandstoneCoastal sand and Alluvium

Hiliimllt Estuary\WaterbodyTeri sandFault/major fractures

-- State boundaryo77 130

10

. _urichi

T M L N DU

77 I 00

ea

Study area

Z ~ India WFig Map of th e s tudy area showing sampling locations

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26scooped up from mid streams or the concave side of streams. The beachsand samples were collected from low water mark after removing a fewcentimeters of surface sediments. All the samples were panned at eachlocation itself, before transferring them to polyethene bags havingappropriate labels. Sample collection was carried in different stagesduring 1998 and 1999 period.

3.2 ILMENITE SEPARATION

In the laboratory the samples were repeatedly washed after treating themwith dilute hydrochloric acid to remove traces of shell or organic matter.The dried -samples were sieved using a Re-Tap Shaker at phi interval r 15 minutes each Carver, 1971 . The opaque rich sieve fractions fromeach sample were made free of magnetite using a hand magnet. Thesesamples were fed to a Frantz Isodynamic Separator 200 forward and side slopes at amperages of 0.1-0.3 at the Centre for Earth ScienceStudies. The ilmenite thus obtained was further purified manually underan optical microscope and a pure crop of the mineral was separated.

The ilmenite from the deposits of Chavara and Manavalakurichi weresplit into differently magnetic frac tions by separating them underprogressively increasing amperages. Magnetic fractionation of ilmenitehas had proved to be an effective method to study the progressivealteration in a deposit Subrahmanyam et al 1982; Frost et al 98 ;Suresh Babu et al 1994 . This approach yeilds i lmenite fract ionsbelonging to the entire spectrum of alteration ranging from those rich iniron to the leucoxenised varieties.

Commercial grade ilmenite from the Chavara deposit was separated in apilot plant scale again into seven fractions based on their magneticsusceptibility by means of a Carpco Magnetic Separator. Out of these

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27IREl represents ilmenite grade, IRE2-4 rutile grade, while the last threefractions correspond to leucoxene. This was carried out to study thedifferently altered fractions of ilmenite from an industrial print of view.Such studies will complement the efforts to produce homogenous oregrades and also in adopting suitable processing techniques.

3 3 X Y N LYS S

The X-ray diffraction analysis is used in the identification of differentmineralogical phases present in a minera l sample and their crystalstructure. Variation of the lattice parameters and changes in crystallinitycan be determined by this method.

Selected samples collected from different environment were finelypowdered in an aga te mor tar . The samples so powdered were on amounted Phillips Diffractometer with CuKa target and Ni filter keeping values in the range of 20>-600 . The reflections caused to the X-rayswere recorded in the form of peaks of different heigh ts on the recordingstrip chart. The heights of the peaks are proportional to the intensity ofreflection. The individual peaks characteristic of each mineral phase wereidentified by comparing the d values with standard JCPDS files. Basedon the X data the following analyses were carried.

3 3 emiqu ntit tive determin tion

The semi quantitative measurement of the mineral phases was carriedout by measuring the area of each identified peak using a planimeter. Thearea thus determined is proportional to the quantity of the phasesavailable Ramakrishnan et al 1997 .

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3.3.2. Measurement o f l a tt ic e p a r a m e te r s

The unit cell lattice parameters like the a . c and values werecalculated from the XRD data Cullity, 1978 . S uc h s tu di es reveal theinfluence of weathering on the structure of the mineral ..

3.3.3 Crystallinity index

This factor indicates the degree of crystallinity of the mineral grains. Asthe well crystalline ilmenite undergoes alteration to secondary productslike pseudorutile or rutile, the crystalline nature is changed and lessdefined. The crys tallinity index = A B/At where A and are the peakheights of two nearby reflections of the same phase from the bottom ofpeaks and is the peak height from the back g ro u nd . T h ese indices werecalculated for certain samples, particularly w he n g ra in s of the same sizegrade or of the same separating amperage.

3.4 STUDIES ON MAGNETISM OF ILMENITE

The magnetism of ilmenite is studied since it has implications ofweathering on the mineral and the consequent compositional changes, Inaddition, t he m ag ne ti c p ro pe rt ie s of the mineral would b e rele van t i n theadoption and upgradation of the industrial processing of ilmenite.

3.4.1 Magnetic fractionation in Isodynamic Separator

The different magnetic fractions of ilrrenite samples were separated outusing Frantz Isodynamic Separator, by varying the amperage of theinstrument. Samples of different size grades were fed to the machine tounderstand th e dependence of m a gn et ism o n the textural characters. The

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mass magnetic susceptibility was calculated us ing the empirical formulaofFlinter 1959

K 20sinB l0 6 hm - , w/2m =mass magnetic susceptibilitye =angle of the side slope and = current in amperes

3.4.2 Magnetic analysis using Bartington Malletic SusceptibilityMeter

The accurate measurement of selected samples was carried out usingBartington Magnetic Susceptibility Meter. This is one of the mostsensitive instruments available for t he dete rminat ion of magnetismDearing, 1999 .

A calibration sample is provided which contains a mixture of 10/ 0magnetite and alumina tightly packed together. The sensor of thesusceptibility meter is calibrated for a sample mass of 10 g. The ilmenitesamples to be analyzed are packed into standard sample pots usingpolythene bags. The analysis by the instrument was carried out in th emode of 0.1 range of measurement. The susceptibility meter was firstllowed to thermally equilibrate with the room t empera ture . Blankmeasurements were carried out before and after the samplemeasurements to eliminate the small var ia tions of instrumental driftbetween the readings. The measurements were repeated for each sampleand the mean value is taken.

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The mass specific magnetic susceptibility is measured by the formula,Mass specific magneticsusceptibility, x = measurement reading x calibration mass / mass

of the sample

3.5 MCSSBAUER SPECTROSCOPY

The different stages of alteration and their chemical composition cannotbe completely estimated by XRD analysis, because of the diffused ratureof the XRD curves of these phases. Another useful parameter for thi s sor tof study is th e determination of the degree of isomorphous latticereplacement and quadrupole shifting of ferrous and ferric ions Gibb et al,1969; Kopcewicz, 1994 . Such analysis using Mossbauer techniqueswould give an idea about the phase changes in ilmenite alteration.

Messbauer measurements were made with a standard PC-basedShirnadzu model operating at the constant acceleration mode. Theradioactive source was a 5mCi5 o in Rh matrix 25 cm away from theproportional gas counter. Absorbers were made by pressing atO.5KN/cm2 circular discs and land 1 cm diameter, containing 100 mg ofboron nitride into which 30 mg of sample was finely mixed. Thespectrometer was cal ibra ted using 25 cm thick natural iron foil. Themeasurements were carried out in transmission geometry at roomtemperature. The data obtained were fitted using a least squares fittingprogram assuming Lorentzian line shape.

3.6 THERMOGRAVIMETRIC STUDIES

Selected samples from different weathering environments were finelypowdered using an agate mortar. About 20-50 mg. of each sample weresubjected to thermogravimetric analysis in a Shimadzu TGA SOH at aheating rate of 10C/minute to a maximum temperature of 100 C. The

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31data obta ined in the form of curves indicate the weight change sufferedby the mineral under increasing temperatures. This would depend on th estructural changes associated with weathering like the alteration phasesformed and the resultant inclusion of water in the mineral structureSuresh Babu et al , 1994; Ramakrishnan et al 1997 . Different magneticfractions of selected samples were analyzed by this method to understandthe behaviour of ilmenite during varying alteration stages under hightemperatures.

3.7 CHEMICAL ANALYSIS

The chemical analyses inc lude those of the major e lements iron andtitanium and the minor and trace elements AI Si, V, er Mn Mg, Zn Ni, Cu. The trace elements were selected on the bas is of their relevance asindicators of provenance alteration chemical changes and economicimportance.3.7.1 Major elements

Wet chemical methods were followed to determine the major elements Feand Ti based on Vogel 1961 . Ferrous iron in the mineral i s determinedto understand the effect of alteration on the oxidiation state of themineral.

About 0 5 gm of finely powdered sample was fused with 1015 gm of thesulphate after melting and cooling the salt first. The fusion wasconducted initially at low temperature. The tempera ture was graduallyincreased to maximum. The crucible was kept at this temperature9 0C for 20-30 minutes. The crucible was cooled and placed inside abeaker containing 2 H2S04 and heated till the dissolution is complete.The solution was cooled and made up to 5 ml.

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32 Estimation of total iron: 25ml of the sample solution was pipetted outinto a conical flask and 5ml of con HCI added and heated to 80CFreshly prepared stannous chloride solution was added to reduce theiron in solution until t he yellow colour of th e solution disappears Thesolution was rapidly cooled to 20C The excess stannous chloride wasremoved by adding 10ml of saturated g I ~ A silky white precipitate ofmercurous chloride results About 5ml Con 1-12804 and 10 drops of N-phenyl anthranilic acid ind icato r a re added after 4 5 minutes This istitrated against standard potassium dichromate solution The end pointis the appearance of a permanent pink colour

The percentage of total iron is calculated as

Total Iron ) volume I

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33iii Estimation of titanium dioxide: This method is carried out in anapparatus, which consists of a 500ml Erlenmeyer flask and a two holedstopper A pointed glass rod is placed in one hole and the o ther one holdsthe short end of a delivery tube.

About 1 ml of the fused solution is taken in the flask and added ISmlcon H2S 4 some distilled water is added. The solution is boiled 2gm ofAl foil is attached to the glass rod of the apparatus. The flask isimmediately closed with the rubber stopper and the free end of thedelivery tube is placed inside a beaker of sodium bicarbonate solution.When all the aluminum is dissolved, the solution is gently boiled

The flask is suddenly cooled The carbonate solution is drawn to the flaskand gives the necessary C02 Atmosphere. The flask is cooled and thestopper removed. The solution is titrated against standard ferricammonium sulphate solution with 4 ammonium thiocynateindicator

volume of titrant x factor x250x 100weight of the sample x volume of solution pipetted

Factor of ferric alum = volume of alum pipetted out x wt. ofstandard Ti 2 x assay of Ti02250 x volume of titrant x 100

3 7 2 Minor and Trace element analysis

The samples were fused with potassium bisulphate as described aboveand dissolved in 200 0 nitric acid Darby and Tsang, 1987 . The standardsolutions of various concentrations were prepa red. They were fed toSartorius model Atomic Absorption Spectrophotometer. The absorbancevalues were plotted against concentration. The absorbance of the sample

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solution was noted from the graph and it s concentration determined Theinstrument was set in characteristic wavelengths depending on the traceelements to be detected while the readings were taken

3.8 MI ROS OPI STU IES

Scanning electron microscopy has become an essential tool in themicromorphological investigation of the mineral and it s alterationfeatures. Such studie s a re impor tant to delineate the environment ofweathering and transportation and the subsequent alteration Krinsely Doomkamp, 1973 .

The samples were boiled with con hydrochloric acid for ten minutes andwashed with distilled water They were then treated with stannouschloride solution for twenty minutes to remove iron oxide coatings About15 2 grains were selec ted randomly for each sample The grains werearranged in rows over the SEM stubs using a double s ided s tick tape Athin layer of conducting silver paint was applied to the bottom of thegrains for better conduct ion The specimen was coated with goldpalladium alloy in a vacuum evaporator The sample was then scannedusing stereoscan The shape relief orientation and density ofdistribution of various features in the different grains were studied andsuitablyfilmed.

Observation of ilmenite grains under ore microscope was carried out tostudy the alteration patterns as well as the intergrowths Selected grainsw r mounted on a polymer resin It was then polished initially bycarborandum paper The grains were further polished on a velvet clothusing alumina solution This was done till the grains became scratchlessand reflecting.