3. ANÁLISIS EXTERNO
3.3. Análisis de la competencia
characterization of olivine sample, supplied from Alfa Olivin A.Ş. in Muğla/Köyceğiz, was made by several methods. The characterization works stated that sample has ultramafic rock origin. Olivine and pyroxene (orthopyroxene and clinopyroxene) minerals were found to be major constituents in addition to chromite in minor scale as opaque phase. Such formation was defined as a rock having a harzburgite-lherzolite constituent.
Chemical analysis of olivine sample stated that major elements are Mg, Si and Fe (Table 1). Such a high Mg and Si
content means that Köyceğiz olivines already meet the specifications of metallurgical use [Acar, 2003; Kleiv and be lower than 3%, which was around 4%
in Köyceğiz olivines [Örgün and crystalline phases observed are enstatite and lizardite. Augite was hardly discriminated on the diffraction pattern.
Lizardite, one of the secondary phase, was visualized especially by its high-intensity line at 12.04° 2θ. Lizardite is the first mineral of the alteration product observed in the serpentinization process [Gürtekin and Albayrak, 2006].
Pure and unaltered olivine does not contain crystal water (Wells, 1959), which increases depending on the alteration rate. Presence of lizardite peaks on the XRD pattern (Figure 1) indicates studied olivine sample does not meet LOI
specification for metallurgical application areas in the present form, and needs to be concentrated. It is expected to be lower than 1% to reduce energy consumption required for endothermic reactions proceeding in the dehydration-calcination processes.
Lizardite, present in the olivine ore as an alteration product, has lower hardness than olivine (Table 2) while hardnesses of other minerals constituting ore are closer to that of olivine [Acar, 2003; Davis, 1977; King, 2009]. Data given in (Table 2) shows that LOI value of sample depends only on grade of lizardite.
Therefore, preconcentration was thought to be possible only applying comminution process due to reasonable difference between the hardnesses of
lizardite and other minerals constituting the ore.
Figure 1: XRD pattern of olivine sample
Table 2: Theoretical chemical composition and hardness of minerals constituting the studied olivine ore [www.mindat.org, www.webmineral.com]
Mineral Chemical Formula Elements, % Mohs
Hardness
Mg Si Fe Ca Al
Olivine (Mg,Fe)2SiO4 25,37 18,32 14,57 - - 6,5-7,0
Forsterite Mg2SiO4 34,55 19,96 - - - 7,0
Enstatite Mg2Si2O6 24,21 27,98 - - - 5,0-6,0
Augite (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 9,26 22,58 4,73 15,26 4,57 5,5-6,0 Lizardite Mg3Si2O5(OH)4 26,31 20,27 - - - 2,5 Crushing operation was the first stage of
comminution. Sample was crushed using a laboratory type jaw crusher down to -1cm. Effect of crushing on preconcentration in certain size fractions was evaluated by chemical analysis and LOI tests (Table 3, Figure 2). Survey of (Table 3) pointed out that chemical composition of the fractions of classified sample did almost not differ from each other. Moreover, preconcentration of lizardite was not observed except the sharp increase in LOI value at finer sizes.
Significantly high LOI value at the -38 µm fraction indicates selective comminution and lizardite accumulation at finer sizes. But, amount of this fraction left at negligible rate, and removal of it
does almost not change the LOI value of coarse fraction. Then, this fraction was not separated from rod mill feed.
Table 3: Chemical analysis of classified jaw crusher product at certain size fractions
Size fraction µm
Weight
%
MgO
%
SiO2
%
Fe2O3
% +1180 77.17 48.06 39.63 8.81 -1180+212 11.76 46.31 38.52 8.87 -212+75 5.70 47.24 38.32 9.31 -75+38 4.25 47.79 38.45 9.32 -38 1.12 47.70 38.73 8.38 Grinding process was applied to obtain -212 µm size product. Prior to grinding,
finely sized fraction (-212 µm) of crusher sample was removed from mill feed by sieving to avoid over-grinding.
Classification of ground olivine was performed by using test sieves at coarse sizes (+38 µm), and by applying gravity sedimentation method at fine sizes (-38 µm). (Table 4) shows the results of size analysis of ground olivine: about 20% of sample was at -38 µm, and 80%
at -121 µm. LOI values given in the table pointed out that selective grinding occurred and, serpentinized portion of sample concentrated at -38 µm size fraction [Jasieniak and Smart, 2010;
King, 2009]. LOI value of the -53+38 µm size fraction does not satisfy the specification for metallurgical applications, which is higher than 1%. On the other hand, the +38 µm size ground olivine was found to meet the LOI specifications whereas fine fraction (-38 µm) has significantly high crystal water.
Figure 2. Variation of LOI of jaw crusher product with size distribution
XRD patterns were also recorded to clarify the effect of hardness on the grindability of Köyceğiz olivines (Figure 3). As compared with the XRD pattern of raw olivine sample (Figure 1), variation at 12.04° 2θ became apparent (Figure 3).
This peak belongs to lizardite [Whittaker and Zussman, 1956]. On the other hand, one of the easily detectable olivine peaks is at 36.44° 2θ. Intensity of this peak did not change noticeably depending on the
particle size of the ground olivine. But, interesting situation was that the intensity rates of these two peaks increased at finer sizes. This result was attributed to the increase in LOI values at finer sizes, and therefore increases in the concentration of serpentinized-soft altered minerals in the finely sized fractions.
Table 4. Size analysis of rod mill product, and LOI data
Size fraction
µm
Weight
%
CO*
%
LOI
%
CO*
LOI
% 212+150 10.36 10.36 1.03 1.03 150+106 16.58 26.94 0.86 0.93 -106+75 18.37 45.31 0.84 0.89 -75+53 15.6 60.91 0.92 0.90 -53+38 18.82 79.73 1.20 0.97 -38+20 18.86 98.59 3.09 1.38 -20+5 1.18 99.77 4.56 1.41 -5 0.23 100.00 7.20 1.43
*: Cumulative Oversize
Figure 3. XRD patterns of high LOI value-finely sized ground olivine samples
classified at (a) -38+20 µm, (b) -20+5 µm and (c) -5 µm size fractions
Chemical analysis of each size fraction of the ground ore sample exhibited similar classified rod mill product depends on the grade of olivine and augite. Hardnesses of these minerals are much closer to each other. Then, selective grinding of augite is not expected, and negligible increase in Fe2O3 content at finer sizes was not taken into consideration. Ca and Al grades of classified fractions did also verify this finding. Such a negligible variation was related with the fundamental principle of comminution: breakage rate of relatively weaker material increases. [Tong et al., 2013; Velázquez et al., 2008].
LOI value of each fraction was evaluated in relation to the hardnesses of minerals constituting the ore (Table 2): hardness of lizardite is 2.5 while olivine and pyroxene minerals have a hardness value between 5-7 [Acar, 2003; Davis, 1977;
King, 2009]. Therefore, grade of lizardite increased at finer sizes as a result of reasonable difference between their hardnesses. Experimental works revealed that preconcentration of olivine is possible at coarser sizes by separating the lizardite-rich fine fraction (-38 µm) (Table 6). Although this work does not cause any significant chemical differentiation between coarse and fine fractions, significant variation in LOI data was observed.
Preconcentration of Muğla/Köyceğiz olivines was investigated by comminution. Chemical and mineralogical characterization of the olivine sample revealed that the sample contained hard (olivine, forsterite, enstatite, augite) and soft (lizardite) minerals. Grade of lizardite was a measure of LOI while Fe content of the sample depended on the grades of olivine and augite. It was stated by comminution-classification works that lizardite liberates selectively at finer sizes, and an olivine preconcentrate having low LOI could be obtained by classifying ground olivine ore. Significant Fe accumulation in the ground-classified products was not observed. End product satisfying specifications of chemical composition for industrial consumption areas could not be obtained by comminution due to closer hardnesses of enstatite, augite, forsterite and olivine minerals.
Table 6. Oxide analysis and LOI values of raw and ground-classified olivine samples
Acknowledgements: The authors acknowledge the grant (Project No:
2013/55) provided by Muğla Sıtkı Koçman University Scientific Projects Unit.
REFERENCES
Acar, B., 2003. Olivinin Sanayiye Yönelik Kullanım Özelliklerinin Tespiti: Çayırbağı (Konya) ve Kızıldağ (Akseki) Olivinleri.
Yüksek Lisans Tezi, Selçuk Üniversitesi Fen Bilimleri Enstitüsü, Konya.
Davis, E.G., 1977. Beneficiation of Olivine Foundry Sand by Differential Attrition Grinding, US Patent No.4039625, 5 p.
Cho, H. and Luckie, P.T., 1995. Investigation of the Brakage Properties of Components in Mixtures Ground in a Batch Ball-and-Race Mill, Energy and Fuels, 9, 53.
Facer, R.A., 2007. Industrial Mineral Collectors. Physicochemical Problems of Mineral Processing, 31, 99.
Gürtekin, G. and Albayrak, M., 2006. Antigoritin Isıl Reaksiyonu: XRD, DTA-TG Çalışması, MTA Dergisi, 133, 37.
Jasieniak, M. and Smart, R.C., 2010. Surface Chemical Mechanisms of Inadvertent Recovery of Chromite in UG2 Ore Flotation:
Residual Layer Identification Using Statistical ToF-SIMS Analysis, International Journal of Mineral Processing, 94, 72.
Jolsterå, R., 2010. Reactions at the Water-Mineral Interface of Olivine and Silicate Modified Maghemite, Luleå University of Technology, 53 p.
King, R.J., 2009. Olivine Group, Geology Today, 25(5), 193.
Kleiv, R.A. and Thorhnhill, M., 2011. Dry Magnetic Separation of Olivine Sand.
Physicochemical Problems of Mineral Processing, 47, 213.
Krivolutskaya, N.A. and Bryanchaninova, N.I., 2011. Olivines of Igneous Rocks. Russian Journal of General Chemistry, 81(6), 1302.
Örgün, Y. and Erarslan, C., 2012. 21. Yüzyılda Olivin ve Türkiye’nin Olivin Potansiyeli, Madencilik Türkiye, June, 62.
Tong, L., Klein, B., Zanin, M., Quast, K., Skinner, W., Addai-Mensah, J. and Robinson, D., 2013. Stirred Milling Kinetics of Siliceous Goethitic Nickel Laterite for Selective Comminution, Minerals Engineering, 49, 109.
Velázquez, A.L.C., Menéndez-Aguado, J.M., and Brown, R.L., 2008. Grindability of Lateritic Nickel Ores in Cuba. Powder Technology 182(1), 113.
Wells, W.G., 1959. Olivine Uses and Beneficiation Methods. NCSU Mineral Research Laboratory Bulletin, 1(2), 1.
Whittaker, E.J.W. and Zussman, J., 1956. The Characterization of Serpentine Minerals by X-Ray Diffraction, Mineralogical Magazine, 31, 107.
www.mindat.org www.webmineral.com