Characterization and Breakdown of South Gabal EL A’urf Polymineralized ore Material

The polymineralized ore material of south Gabal El-A’urf area hosts several economic minerals. These include tanteuxenite, monazite, bastanasite, anatase, as well as zircon. The corresponding interesting rare metals of these minerals include Nb, Ta, lanthanides (REE), Ti, and Zr. Different breakdown techniques have been investigated namely; agitation, pug and fusion. The latter technique is found to be preferred under the following conditions; potassium bisulphate ore/reagent weight ratio of 1/3 at 650 ºC for 3h. The realized dissolution efficiencies for all metal values were as follows 98.0% and 99.3% for Nb and Ta respectively as well as complete dissolution for lanthanides (REE) and 94% for Ti while Zr did not exceed 20% and concentrated in the residue left behind. This study of breakdown techniques aims to characterization of ore material of south Gabal El-A’urf area as well as preparing a proper leach liquor suitable for further recovery procedure and obtain pure remarket able products.


Introduction
A polymineralized ore material has been lately reported in south Gabal El-A>urf area, central Eas-tern Desert, Egypt [1]. This mineralization includes tanteuxenite, monazite, bastanasite, anatase and zi-rcon. The corresponding interesting rare metals of these minerals include Nb, Ta, REE, Ti, and Zr. The present work has been oriented towards the charact-erization of this mineralization mineralogically and chemically. For this purpose, a technological sample was properly collected and first subjected to mineraalogical study to identify its mineral constituents as well as possible separation of certain mineral in cer-tain size fraction, then applying different breakdown techniques for preparing a proper leach liquor suita-ble for further separation and recovery procedure.
Several studies have been applied on such ore material; Shaw and Lindstrom [2] recovered the metal values of the euxenite mineral by fusion with (NH 4 ) 2 SO 4 or (NH 4 )HSO 4 at 400 °C for 4 hours.
Shaw [3] indicated that euxenite from Arizona is amenable to REE recovery by digestion with HF-H 2 SO 4 acid mixture. Shaw and Bauer (4) treated Id-aho euxenite by H 2 SO 4 acid alone for REE recovery. Pittuck et al [5] performed caustic fusion process for euxenite and fergusonite that assayed 9.4% U 3 O 8 and 12.4% Nb 2 O 5 at 700 °C for 10-15 min with S/R ratio 1/3. El Hazek [6] studied the recovery of valuable metals from polymineralized ore material contain-ing samarskite, betafite, thorite, uranophane and ziarcon. The ore concentrate assayed 31.77% RE 2 O 3 , 20.78% Nb2O5, 9.09% ZrO 2 , 6.45% ThO 2 , 2.2% U 3 O 8 and only 1.06% Ta 2 O 5 as well as 0.33% TiO2. This ore material subjected to H 2 SO 4 agitation leac-hing to dissolve U, Th and REE while keeping Nb, Ta, Ti and Zr in the residue for subsequent leaching by HF. Moreover, El Hussaini and Mahdy [7] have been studied the recovery of different metals from ore material containing fergusonite and euxenite be-side the refractory U mineral davidite. Using agi-tation H 2 SO 4 /HNO 3 acid mixture, almost complete leaching of Nb and Ta was obtained together with 86% of Th and 70% of the REE, however, U and Ti leaching efficiencies did not exceed 60%.

Ore Characterization
Mineralogical composition of south Gabal El-A'urf ore material To identify the economic mineral constituents of south Gabal El-A>urf ore material, a representative bulk heavy fraction (bromoform) was examined by X-ray diffraction technique (XRD). Using Philips x-ray diffractometer, model PW 223/20 in which the copper tube was operated at 49 Kv and 20 mA. Possible physical upgrading of certain mineral in certain size fraction was investigated where each of the obtained size fractions was ground to -200 mesh, attacked by a mixture of acids and analyzed for the interesting metals.

Chemical composition of south Gabal El-A>urf ore material
The representative sample of the studied south Gabal ElaA>urf ore material was first ground to a 200 mesh grain size and analyzed for its major and trace elements constituents using aqua regia and ac-ids mixture. In the meantime, a total loss of igniti-on obtained at 1000 °C. This loss corresponding to humidity, combined water, CO 2 as well as possible organic matter.

Ore Breakdown (Leaching) Procedures
The ore sample was ground to pass -200 mesh sizes (65µm) and mixed well. After quartering, se-veral representative sample portions were taken for study leaching experiments where three ore breakd-own techniques have been applied namely; sulfuric acid agitation leaching, sulfatizing roasting (pug le-aching) and potassium bisulfate fusion.

H 2 SO 4 acid agitation leaching
Each leaching experiment has been performed by agitating a weighed amount of the ground sample with the acid of different concentrations with diffe-rent solid/liquid ratios for different time periods at different temperature degrees. In these experimen-ts, a hot plate with magnetic stirrer were used and precautions were taken for avoid evaporation. The obtained slurry then cooled, filtered, washed with distilled water and made up to volume. The residue left behind was subsequently dissolved in concent--rated HF, filtered, washed with distilled water and made up to volume, then both solutions analyzed to calculate the dissolution efficiency percent accordiang to the equation:

% Leaching efficiency
Sulfatizing roasting (pug leaching) Sulfatizing roasting experiments were applied using conc. H 2 SO 4 where a weighed portion from the finely ground sample mixed well with a proper amount of conc. acid in glass watches and allow-ed for roasting at different temperature degrees in a muffle furnace for certain time. The obtained paste was then cooled and agitated with 2N H 2 SO 4 in a S/L ratio of 1 : 2.5 for 3 hrs at 300 °C. After cooling, the slurry was filtered, washed with distilled water, made up to volume for analyzing the dissolved met-al values and calculate the dissolution efficiency.

Bisulfate fusion
Several fusion experiments have been performed using KHSO 4 . In these experiments, different amou-nts of KHSO 4 were mixed with sample portions in a porcelain crucibles for different time periods and di-fferent temperature degrees. The obtained melt was then cooled and washed with distilled water, filtered and made up to volume for analyzing the interesting metal values and calculate the dissolution efficiency percent.

Analytical Procedures
Determination of the interesting metal values whether in the original sample or during processing streams will be summarized as follows: Ti, Nb, Ta and Zr were analyzed by the atomic absorption tec-hnique using a Unicam model 969 (Nitrous-Air ace-tylene flame), auto gas box at the wavelengths 365.4 nm 334.4 nm, 271.5nm and 360.1nm respectively. (Weltz and Sperling 1999) [8]. A spectrophotometric method using a double-beam UV-Visible Shimadzu (model 160A) was applied for REE where they form stable colored complex with Arsenazo III in weakly acidic media at pH about 2.6 and the absorbance me-asured at wavelength 650 nm against a reagent bla-nk solution (Marczenko,1986) [9]. Ca and Mg were determined by a titrimetric method using EDTA. Na and K were determined by flame photometry.

Metal concentration in the leach liquor
Original metal concentration in the ore = × 100

Mineralogical composition of south Gabal El-A'urf ore material
To identify the economic mineral constituents of south Gabal El-A>urf ore material, a representative bulk heavy fraction (bromoform) was examined by XRD. From the obtained data, it was found that the principal minerals involve ASTM [10] tanteuxenite 8-293, monazite 11-556, bastanasite 11-340, anatase 21-1272, and zircon 6-0266. In other words, it can be mentioned that Nb, Ta and some of REEs are fou-nd in tanteuxenite mineral while the rest of REEs are found in both bastanasite and monazite. Ti is found as anatase while Zr is found as Zircon.
Possible physical upgrading of certain mineral in certain size fraction was investigated by sieving a representative portion of the ore material with a set of sieves ranging from 500 µm down to 100 µm (+35 to -140 mesh size), each of the obtained size fr-actions was ground to -200 mesh, attacked by acids mixture and analyzed for the interesting metals. The obtained data are tabulated in Table (  From the obtained data, it is clear that no prefer-ential concentration of any of the interesting metals in certain size fraction since their assay is almost comparable in.

Chemical composition of south Gabal El-A>urf ore material
Chemical composition of south Gabal El-A>urf ore material shown in Table (2) showed that the ore material is mainly composed of SiO 2 beside Al 2 O 3 and Fe 2 O 3 that attained 5% and 5.1% respectively as well as high K 2 O content (4.92%). In the meantime, a total loss of ignition of about 0.74 was obtained at 1000°C. This loss corresponding to humidity, com-bined water, CO 2 as well as possible organic matter. On the other hand, analysis of the economic trace metals involved RE 2 O 3 1.9%, Nb2O5 1.25% as well as TiO 2 and ZrO 2 1.23% and 1.12% respectively beaside Ta 2 O 5 0.13%.

H 2 SO 4 acid agitation leaching i-Effect of H 2 SO 4 acid concentration
A set of leaching experiments have been perfo-rmed using different concentrations of H 2 SO 4 acid ranging from 200 to 1800 g/l. The other leaching conditions were fixed at 300 °C for 3h with S/L ratio of 1/3. The obtained leaching efficiencies plotted in Fig. (1) showed that REE and Ti increased from 55.7 to 81.0 % and from 62.2 to 84.8 % respectively by increasing the acid conc. from 200 to 800 g/l. Furt-her increase in acid concentration keeps comparable results for REE and Ti leaching efficiencies.
However, Zr leaching efficiency didn't exceaed 10.55 % as it requires higher temp. more than 300 °C. On the other hand, Nb and Ta bad dissoluti-on necessitates the presence of HF acid or much se-ver conditions to breakdown the mineral lattice and facilitate their dissolution.  The effect of S/L ratio (ore/ H 2 SO 4 acid ratio) upon the dissolution of the interesting metals was studied with S/L ratios ranging from 1/1 to 1/5 us-ing 400 g/l H 2 SO 4 acid at 300°C for 3h. Leaching efficiencies plotted on Fig.(2) indicated that 400 g/l H 2 SO 4 cannot breakdown the Nb-Ta mineral latti-ce even at 1/4 S/L ratio. In the meantime, REE and Ti dissolution efficiencies increased to 73.00 % and 78.9 % at 1/3 S/L ratio and almost kept steady at S/L ratio of 1/4.

iii-Effect of leaching temperature
The effect of leaching temp. has been investigated at temperature degrees ranging from 150 up to 350 °C under other fixed conditions of 400 g/l H2SO4 conc., S/L ratio of 1/3 and leaching time 3h. The data obtained illustrated on Fig.(3) indicated that the ref-ractory nature of the poly-mineralized ore material has required high temp. up to 350 °C to be broken. So the ore breakdown requires either higher temp. than 350°C or using HF acid to facilitate the minerals breakdown. However, partial separation of Nb, Ta & Zr from REE and Ti could be achieved at 300 °C.

iv-Effect of leaching time
A set of leaching experiments has been perfor-med at different times ranging from 1 to 4 h. The other leaching conditions fixed at H2SO4 conc. of 400 g/l, 1/3 S/L ratio at 300 °C. The correspondi-ng leaching efficiencies plotted in Fig. (4) indicated that the polymineralized ore material required long leaching periods, where REE and Ti leaching efficaiencies were 45.1 % and 53.0 % at 1 h. Extending leaching time up to 3 and 4 h increased the leaching efficiencies of REE to 73.8 and 79.8 % respectively while Ti increased to 78.8%. Noticed that Nb and Ta leaching efficiencies began to appear at 4 h.
v-Effect of HF acid addition A series of leaching experiments has been perf-ormed with HF addition (to H 2 SO 4 ) with S/L ratios ranging from 1/1 to 1/5 of the ore weight to impro--ve Nb & Ta dissolution efficiencies. The other fixed leaching conditions were 400 g/l H 2 SO 4 conc., S/L ratio of 1/3 at 300 °C for 3 h. The corresponding leaching efficiencies plotted in Fig. (5) showed the importance of HF acid addition to bring out almost complete dissolution of Nb and Ta where they atta-ined 95.00 % and 94.00 % respectively at S/L ratio of 1/5 but with partial precipitation for REE and Ti while keeping Zr not affected.
Finally, from the foregoing agitation leaching st-udy, it can be concluded that this technique is not efficient in dissolving most of the interesting metals from south Gabal El-A>urf polymineralized ore ma-terial. Otherwise, the sulfate leach liquor should be separated before the HF addition to keep REE and Ti contents, also to dissolve Nb and Ta in separate HF leach liquor.  [11] and/or other impurities which would increase using concentrated acid (Terry) [12]. ii-Effect of curing time A set of leaching experiments has been performed at different time periods ranging from 2 to 10 h. The other leaching conditions were fixed at H 2 SO 4 amou-nt of 10 ml at 350 °C. The obtained results plotted on Fig. (7) showed that the dissolution efficiencies of all interesting metal values increased by increasing cu-ring time till 6 h. where Nb attained 30.1 %, Ta 26.7 %, Ti 89 % , REE 76.00 % and Zr 11.6 %. After 6 h, the dissolution efficiencies of all metal values began to decrease most probably due to hydrolysis.
iii-Effect of curing temperature A series of pug leaching experiments has been applied using different curing temp. degrees ranging from 150 to 350 °C. The other leaching factors were fixed at acid volume of 10ml for of 6 h curing time.
The results plotted on Fig. (8) proved increasing the dissolution efficiencies by increasing temp. to 350 °C for all metals where Nb attained 30.1%, Ta 26.7 % , REE 76 % , Ti 89 % and Zr 11.6 %.  ii-Effect of fusion temperature A series of experiments has been studied at temp. ranging from 350 °C to 750 °C. Other fusion con-ditions were fixed at ore / KHSO4 ratio of 1:3 for 3h. The dissolution efficiencies of metals, plotted on Fig. (10), increased gradually by increasing fusion temp. from 350 to 650 °C where they attained com-pletion for Nb, Ta & REE with Ti 94 % and Zr 20 %. These data indicated that fusion temperature is the most important factor for ore breakdown. However, increasing the fusion temperature to 750 °C has an adverse effect on the dissolution efficiencies of the studied metal values where the dissolution efficienacies decreased to 74.1 % for Nb, 77 % for Ta, 89 % for REE & 74 % for Ti. This decrease may be due to hydrolysis. Zr leaching efficiency was only improvaed by increasing temp. where it attained 24.5 %. iii-Effect of fusion time A set of experiments was studied ranging from 1 to 4 h. Other fusion conditions were fixed at an ore / KHSO 4 of 1:3 and fusion temperature of 650 °C. The dissolution efficiencies of the studied interesating metal values are plotted in fig. (11). From the results, it is clearly evident that increasing the fusion time from 1 to 3 h. increases the dissolution efficieancies for all metals where it reached 100 % for REE and 99.3 % for Ta, while reached 98 % for Nb, 94 % for Ti and 20 % for Zr. Further increasing the fusion time to 4 h has adversely affected the dissolution eff-iciencies of all metals except Zr, most probably due to hydrolysis.
From the above studied fusion factors of south Gabal El-A>urf ore material, it can be concluded that the optimum conditions for dissolving the in-teresting metal values can be summarized as ore/ KHSO 4 ratio as 1/3 at 650 °C fusion temperature for 3 h. fusion time.

Conclusion
Ore characterization of south Gabal El-A>urf proved the presence of several economic minerals. These include tanteuxenite, monazite, bastanasite, anatase, as well as zircon. Sieve analysis proved that no preferential concentration of any of the interesti-ng metals in certain size fraction since their assay is almost comparable.
Different breakdown techniques have been inve-stigated upon polymineralized ore material of south Gabal El-A>urf. For agitation leaching by sulfuric acid, the optimum conditions were 400g/l acid conc. at 300°C for 3 h using 1/3 S/L ratio. These conditi-ons realized dissolution efficiences 73% and 78.9% for REE and Ti as well as 10.2% for Zr while keaeping Nb and Ta unleached in the residue. On the other hand, using HF/ H 2 SO 4 acid mixture increases the dissolution efficiencies up to 95% and 94% for Nb and Ta while sharply decreased REE and Ti to 39.50 and49.80 as well as 10.8% for Zr. Otherwise, the sulfate leach liquor should be separated before HF addition to keep REE and Ti contents, also to dissolve Nb and Ta in separate HF leach liquor for further recovery steps.
In the meantime, pug leaching by sulfuric acid, achieved low leaching efficiencies for all elemenats. Otherwise, potassium bisulphate fusion, realized highest dissolution efficiencies for all metals where Nb and Ta attained 98% and 99.3% as well as coamplete dissolution for REE and 94% for Ti while Zr not exceed 20% and concentrated in the residue left behind for further treatment. The optimum con-ditions were 1/3 ore/reagent ratio at 650°C for 3 h. Thus the preferred breakdown technique suitable for this polymineralized ore material is KHSO4 fusion or alternatively successive agitation leaching using H 2 SO 4 acid for REE and Ti then HF acid for Nb, Ta and Zr.