Ilmenite of Black Sand Deposits of Visakhapatnam-Bhimunipatnam Beach, East Coast of India

Indian Journal of Marine Sciences Vol. 12, December 1983, pp.220-222

T RAMAMOHANA RAO, N RANGA RAO & M V RAMARAJU Department of Geology, Andhra University, Waltair 530003

Received II July 1983; revised received 21 October 1983

Ilmenite with its exsolution intergrowth of titanhematite is separated from black sands using a special techhique. Chemical analysis of this crop from 18fractions gives TiO 2 content from 47.14 to 50.74%. The relative concentration ofTi02, as worked out from the data on mineral proportion of ilmenite intergrowth and chemical analysis, amounts to 23.73 kg. (100 kg) -1 bulk sample of the black sands.

Black sand deposits of Visakhapatnam• crucible for 10 min over a bunsen flame and is cooled Bhimunipatnam coast constitute an important source to room temperature. This has destroyed the induced of titanium, which is contained principally in ilmenite artificial diamagnetic property of ilmenite with its with its intergrowth oftitanhematite occurring in these intergrowth, due to the presence of magnetite, while sands. Estimation of the proportion of ilmenite with its the natural magnetic property of magnetite is intergrowth and the content of Ti02 in these deposits unaffected. With a thin piece of wrought iron, the has not been attempted so far because of the difficulty magnetite grains which get attracted to the wire are in the separation of these from magnetite of the bulk removed. The remaining portion of the sample is fed sample in the laboratory. A special technique is used in on the Franz isodynamic separator and ilmenite with the present study to separate the ilmenite with its its exsolution intergrowth oftitanhematite is separated intergrowth of titanhematite from the black sands. as magnetic fraction using 0.3 A of current with 25° Textural analysis and mineralogy of black sand horizontal and 15° vertical tilts of the separator. The deposits of this coast have been studied earlier!. The separated ilmenite with its intergrowths is checked for beach is fairly stable with the SW winds (Jan. to Aug.) leading to accretion and the NE winds (Sept. to Dec.) 83"115' leading to erosion of sand on the foreshore region. Further the high tides during SW monsoon period deposit the sand on the foreshore region while the high tides during NE monsoon remove a substantial amount of sand deposited on the foreshore region. On the backshore region there is little net addition of sand in anyone year as inferred from beach profiles in various studies. Black sand concentration takes place pre• dominantly on the backshore region, and 16 samples were collected from this region in Dec. 1976 along the 24 km stretch of this coast (Fig. I). Size analysis has shown that the black sands comprise 2.52% coarse sand, 26.65% medium sand, 66.8% fine sand and 4.03% very fine sand fractions. The relative proportions of ilemnite and other minerals present in each sieve fraction are estimated. Ilmenite with its intergrowths of titan hematite occurs in the medium sand, fine sand and very fine sand fractions at 20.93, 61.32 and 66.35% y,praCloJiiir' - Harbour respectively by weight. Proportion of this mineral in n~h~/ channel the bulk sample of the black sands works out to be c:::-_~ ConlGln 100melers • .,.-- SlreCln\ 48.41 % by weight . • lto16 sample locations at bloCk sands. Separation method-A known amount of each sieve fraction of black sand sample is first roasted in a nickel Fig.I-Locatiop of samples of black sands i 220 J

I II SHORT COMMUNICA TrONS

purity on polished grain mounts and is found to be Ferrous Fe is determined from a separate portion of 99.9%. each of the 18 fractions (which are previously Analytical method- Ti02 of the ilmenite with its powdered) by permanganate method and the total Fe intergrowths has been determined on 18 fractions as Fe203 is determined by gravimetric method from chosen from 6 samples each represented by the which Fe203 is calculated3. medium sand ( - 500; + 350 and - 350; + 250 flm), fine Ilmenite-Polished mounts of separated grains have sand ( - 250; + 177 and - 177/+ 125 flm) and very fine revealed a variety of exsolution intergrowth textures sand ( - 125/+ 88 and - 88/ + 62 flm) fractions between ilmenite and titanhematite, similar to those adopting the tannic acid method 2. described from Karaikal coast, Tamil Nadu4• Ilmenite

)

Fig.2-Dash-like titan hematite exsolved from ilmenite (SEM, x 980). Fig. 3-Plate-shaped coarse ilmenite (higher relieO exsolved from titanhematite (SEM, x 490)

221 INDIAN 1. MAR. SCI., VOL. 12, DECEMBER 1983

is pleochroic in shades of brown and is strongly i 48.7749.0949.7447.8249.3648.6647.1448.2750.4649.5550.7449.9550.1247.4148.527.49 ' ~" I J M :iI TableIlmenitewithItsExsolutionfractionF202820222131FIlmeniteintergrowths(wt%)1011048,9449.72011893.382240213492.2591.438.420112022491.233030112011232.09092.99IntensityFe203Sand44.5642.399.1789.5244.035.4042.0242.2643.4744.2643.6143.3243.2943.6843.826.9792.5542.1743.207.9543.856.8292.6189.1210.5642.2044.545.3894.0744.2210142.690 l-X-RayFeO10.5510.3011.0610.3489.0610.8510.3510010146.308.579.0288.746.899.7289.247.146.351005.605.947.185.1792.107.415.797.218.0291.498.365.4294.115.766.0293.477.1891.807.93202702241.8434035022727352537112613132028410112505534'd'hkil42.52021.6926011261.4563.6801.4881.3491.6381.313(A.) Ilmenite*Titan- Dataof of IlmeniteTitanhematite Calculatedmineralproportion and Titanhematite (wt%) I Sample*as FeTi03; <5Fe203VFanisotropic+excessTi02 with over shades ilmenite. of grey interference colours. ~ ~ No.39 GrovesM A W, Silicate11165151.628 analysis1.4691.3441.7261.3751.8671.275VFMM(Thomas Murby & Co. London) 4 BandyopadhyayaS,408.5 KrishnaGeol1937,230.theRao rarer SocQ J.s elements India,J Geol R, Sci23(1982)284. Min(CharlesGriffen'-1Cult, Met30 Soc (1964)552.r India,& Co34(1962)163. Ltd, London)1955,1 1.508IntergrowthsF andTitanhematite Calculated2.5403.7302.2302.750M M Proportions of Ilmenite and 2 Schoe1lerWRIlmenite& Powe1lA R, The\ analysis of minerals and ores of References1 Ramamohana'd' (A.) Titanhematite RaoTi02 T, ShanmukhaM= medium;F is Rao =whitish Chfine;VF=& SanyasiRao and very fine; ishkil= K, alsoJ hexagonalnotation strongly 1 \~ hematite6 l \ Table 2-Analysis anisotropic. Scanning electron micrographs of the grains show the fine dash-like titanhematite ex solved J\ from ilmenite (Fig.2) and the plate shaped coarse ilmenite exsolved from titanhematite (Fig. 3). An estimate with the integrated stage on the polished mounts of the separated grains gave an abundance of ilmenite component of the ilmenite-titanhematite intergrowths of the order of 85 to 95%. The exsolution textures of ilmenite-titanhematite of the black sands of this coast suggest a complex history of magmatic and metamorphic events for the source rocks of charnockites and khondalites5. Table 1 gives X-ray diffraction data together with calculated cell parameters of ilmenite and titanhe• matite phases present in the sample. The calculated axial length (hexa~onal notation) of ,a' and 'c' axes are 5.089 and 14.08 A respectively for ilmenite and 5.04 and 13. 786 A respectively for titanhematite which are within accepted limits of values for these minerals. Table 2 gives the composition of analysed ilmenite intergrowths with the calculated amounts (wt%) of ilmenite and titanhematite components from 18 fractions. TiOz content of ilmenite intergrowths varies from 47.14 to 50.74%. The calculated ilmenite component as FeTi03 varies from 88.74 to 94.11%. The calculated titanhematite (Fez03 +excess TiOz over ilmenite) varies from 5.6 to 11.06%. From the above it follows that (i) the proportion of ilmenite component of the intergrowth in any fraction is uniformly high, (ii) there is no significant variation of TiOz between the samples or among the medium, fine and very fine sand fractions of the samples, and (iii) there is an excess of TiOz over calculated ilmenite in each analysis which represents the solid solution part of the calculated titanhematite. The average concentration of TiOz contained in different sand fractions of the non-separated bulk sample of the black sands is calculated from the data on the proportion of ilmenite intergrowth in different sieve fractions of the bulk sample and the chemical data of TiOz of the analysed fractions of the ilmenite intergrowths. It works out that every 100kg of the black sand contains (i) 10.18 kg of TiOz in medium sand fraction, (ii) 30.46 kg ofTiOz in fine sand fraction, and (iii) 32.45 kg ofTiOz in very fine sand fraction. An unsieved black sand sample of 100 kg contains 23.73 kg of TiOz on the average. These studies are relevant in view of the fact that titanium metal, because of its high strength, light weight and resistance to corrosion and titanium oxide because of its versatility as white pigment are finding increasing use in all modern industries.

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