40(2)-08.fm

y, 40«, y, 141-151, 007 Econ. Environ. Geol., 40(), 141-151, 007 p ü w y L- g e w tá Á * w l w Effects of Oxalic and L-ascorbic acids on Iron Removal form Iron-bearing Illite Won-Pyo Lee, Il-Mo Kang and Hi-Soo Moon* Department of Earth System Sciences, Yonsei University This study was focused on iron removal from illite by L-ascorbic and oxalic acids. Iron has been shown as a secondary mineral such as iron oxides and hydroxides in illite ores. It is also known as a primary agent to degrade brightness index of the ores. Methods such as physical separation and chemical leaching with strong inorganic acids have been widely used to remove the iron from the ores. However, these methods are expensive and give rise to environmental problems. In this study, we examined an alternative method using solutions with different set of combination of sulfuric, hydrochloric, L-ascorbic, and oxalic acids. Compared to chemical treatments with only inorganic acids, our results demonstrate that an addition of L-ascorbic acid in inorganic acids results in decreasing both total concentrations of the inorganic acids and time for the treatments. The treatment with 0.15 M L-ascorbic acid and 0.5 M sulfuric acid in solution for 60 min significantly improved the brightness index from 4.4% to 74.4%. This improvement is similar to that of treatment with only.5 M sulfuric acid alone for 150 min. Mineralogical and chemical analyses were performed to compare the effect of acid leaching on illite powders. No obvious differences are observed in the mineralogical characteristics and particle size distributions of the samples. These results suggest that the treatment with the addition of L-ascorbic acid in sulfuric acid could effectively remove iron without modifying the physicochemical properties of illite under conditions used in this study. Key words : Illite, L-ascorbic acid, Oxalic acid, Iron removal, Brightness p w x ww. p Ÿ w w k Ÿ y ƒ. z sƒw» w» (y, ),» (L- g, ), yw (» +» ) w. x 0.15 M L- g 0.5 N y ƒw yw k ww, 60 1.5 wt % y w ƒ z ùkü. 0.5N y w 60 y 0.68% w. y w 1.5wt % y w» w 5N 150. ey š, ey L- g k z w. y z p ƒ 4% 75%, ƒ 10YR 8/4 5Y 8/1 w CBD ƒw. p wš y ƒ s w ù Ÿ w / Áyw p yƒ. p, L- g,, y w, 1. p Grim et al.(1937) w m 4µm w m j» q, q e t w Ÿ ew ( rodo and Eberl, *Corresponding author: hsmoon@yonsei.ac.kr 141

14 tá Á 1984). IMA s w w d K w 0.6 0.85 q p w (Rieder et al., 1998). p Ÿ w p» w Áyw ƒ w. Ÿk ü y w (»,», k,»» ), (m, ),, r p, gq, s,, t, y t š. Ÿ p Ÿ ty w y w y ü, w y p w g š ƒƒe y w ƒ w w. w w k Ÿ y ƒ k.» y» ƒ w, Ÿ œ,, p ù p w g w yw œ.» p t g k ƒ û y w z û» yw» w. ù y j šƒ, wš, s y»w. w p ù p w št z w (Conley and Lloyd, 1970), Ÿ w ƒ w (Cameselle et al., 1997). m w m w p - - k z ù šƒ t eƒ v w» Ÿ w w œ yƒ ƒ w. w y ey z,» w w ƒ z wš.»,, L- g,, s, g w, e ù p k w w» f w w w ƒ y w š (Veglio et al., 1996; 1998; Cameselle, 1997; Ambikadevi and Lalithambida, 000; Mandal and Banerjee., 004). ù p w y x w w, ww L- g ( k C)» w w w. z y ey k C w y p w z sƒw...1. y ty x y w wš p Ÿ w. w 100 mesh w q w z, X- z (MacScience, MXP 18A RINT-500) X- xÿ (Philips Analytical B.V., Philips PW404) w Ÿ w, M 1 x wš w. z w, w 6wt.% d. w z NEWMOD v w M 1 x p yw ql Fig. 1. (a) X-ray diffraction pattern of the untreated illite from the study area. (b) Simulated X-ray pattern for the M 1 type illite with quartz. *Quartz.

일라이트 분체 내에 함유된 산화철 제거에 옥살산과 L-아스코르브산이 미치는 영향 Fig.. 143 Scanning electron microscopic images of untreated illite. Mineralogical and physicochemical characteristics of untreated illite used in this study. Properties Results Color 10YR 8/4 Brightness (%) 4. Mean particle size (µm) 8.47 µm Mineral compositon M illite (~94wt.%), Quartz(~6wt.%) Structural fomula K Na (Al Fe Mg Ti )(Si Fe O * (wt.%) 3.0 *total Fe Table 1. 1 1.47 0.19 치하고 있다(Fig. 1). 채취된 시료는 건조 후 잘 혼합시켜 분체를 만들어 시행한 주성분 원소를 분석결과는 SiO 50.16, Al O 31.3, K O 7.96 그리고 Fe O 는 3.0 wt.%(총 철의 함량)를 함유하고 있었다. 그 외에 Na O 0.71, TiO 0.33, MgO 0.39, P O 0.05, CaO 0.09 wt.%를 소량 하고 함유하고 있다. 석영이 약 6 wt.% 함유되어, 평 균적인 일라이트의 성분에 비해서 상대적으로 Al O 와 K O의 함량은 낮고 SiO 의 함량은 높게 측정되었 다고 사료된다. 평균적인 일라이트의 성분과 비교해 볼 때 산화철의 함량이 3.0 wt.%로 상대적으로 높은데, 3 3 5 3.71 0.18 0.07 0.05 6.37 Al ) O (OH) 1.63 0 4 3 3 적갈색의 산화철 성분은 일라이트 표면을 침착하거나 개개의 일라이트 입자를 교결하면서 분말 내에 함유되 어 있음이 SEM 관찰을 통하여 확인되었다. 입도분포 측정결과 본 일라이트 분체는 약 0.6, 8, 80 µm에서 약한 중간값을 갖는 입도분포를 보였으나 평균 입도는 8.47 µm이다. 전체입자의 약 90%가 45 µm이하로 분 포하였다. 주사전자현미경 (Jeol 5610LV) 관찰결과, Fig. 와 같이 개개의 일라이트 입자는 대략적으로 5 µm 이하의 입자크기를 보이며, 가장자리는 매끄럽지 못하고 톱니 모양인 모습을 관찰할 수 있었다. 입자크 기는 균질하지 않으나 상당수의 입자들이 커다란 집합

144 tá Á x wš. s xk ( w trimodal) w p x w p w w. p w d w, Munsell 10YR 8/4 ùkü. p ƒ y w w wš w. d, t y w 4.%. w w y w p». y t w p, (N8/0) ƒàš 80%. ww p p Table 1, y w p. w m w Ÿ ƒ w wš q ƒ w d y wù, y w ƒ û p ww š... y x p 5g 0 ml ƒw, 80 o C w 40 w.»,», yw w,» 1,, 5N y w š,» 0.15 M L- g w. yw 0.5, 1 N y 0.38 g g 0.53 g ƒw ƒ» 0.15 M ( 4 yw ) k ww.» w x 40 j xk 30 z w,» yw 10 g z w. z xk š w, Ÿ»(Shimazu, AA-6701F) w w w d w z y xk y w. (š ) w w z 80 o C w (Minolta, SPAD-503 Soil Color Reader) (Carl Zeiss, Elrepho) d w. ƒ y w š w š w X- z, X- xÿ, (Malvern instrument, Mastersize 000E), x (JEOL, 5610LV) w p CBD w p w. 3. m 3.1. y x 3.1.1. y w y y 1,, 5 N w, ƒ j w y w d w (Fig. 3a). 1 N y w y w 30 0.77 wt.% 40 1.3 wt.% ƒw. N y 0.91 wt.% 1.45 wt.% w y w ƒw ù, 10 z 1.45 wt.% w w. 5N y 1.7 wt.% 1.5 wt.% d, w Fig. 3. Plots of dissolved Fe O 3 versus reaction time at different concentrations of sulfuric acid(a) and hydrochloric acid(b): Solid circle; 1N, solid diamond; N, and solid rectangle; 5N.

p ü w y L- g e w 145 150 z. w y w, w ƒ w w w» w w. Fig. 3b w, 1 N ƒw 30 0.89wt.% 40 1.8wt.% ƒ w, N 1.3 wt.% 1.55 wt.% ƒw, 5N 1.5 wt.% 1.63 wt.% ƒw ƒ 1.60 wt.% s w. 5 N, 90-10 1.63 wt.%, z ù x 90 z y. N w 180 1.5 wt.% y, z 40 1.56 wt.%¾ ƒ w. w 1N 1.30 wt.% y w 180 z l. 3.1..» w y»» w k z xw» w 0.15 M L- g 0.15 M w y x ww.» w k 10 k, L- g 0.15 M 0.54 wt.% 0.6 wt.% s ùkü, 1.13 wt.% 1.38 wt.% d (Fig. 4a). L- g w 60 z, ü y w s³ 0.6 wt.% w w w š q ù, w y w ƒw. 3.1.3. yw w y y ƒƒ 0.5 N 1 N 0.15 M L- g ƒw k Fig. 4b w. 1N y 0.15M L- g yw, s³ 1.5 wt.% y. 0.5N y 0.15 M L- g yw k y 60 ¾ 1.37Ê1.43 wt.%. 1 N 0.1 wt.% û s ùkþ. w 90 z 1 N s³ 1.5 wt.% w, w. Fig. 4. Plots of dissolved Fe O 3 versus reaction time after treated with acids. (a) Treated with 0.15M L-ascorbic acid(solid triangle) and 0.15M oxalic acid(cross), (b) with 0.15M L-ascorbic acid in 0.5N H SO 4 (solid rectangle), 1N H SO 4 (solid circle), 0.5N HCl(solid diamond), 1N HCl(solid triangle), and (c) with 0.15M oxalic acid in 0.5N H SO 4 (solid rectangle), 1N H SO 4 (solid circle), 0.5N HCl(solid diamond), 1N HCl(solid triangle). w, y w ùk üù, ¼ ùkû. 1.5 wt.% w 0.5 N 1 N 90 d., L- g ƒw y

146 tá Á Table. Munsell notations of illite powders after treated with inorganic acids. H SO 4 HCl process reaction 1N N 5N 1N N 5N time(min.) 30.5Y 8/.5Y 8/.5Y 8/.5Y 8/3.5Y 8/ 7.5Y 8/1 60.5Y 8/.5Y 8/ 7.5Y 8/1.5Y 8/ 7.5Y 8/1 5Y 8/1 90.5Y 8/ 7.5Y 8/1 7.5Y 8/1.5Y 8/ 7.5Y 8/1 5Y 8/1 10.5Y 8/ 7.5Y 8/1 7.5Y 8/1.5Y 8/ 7.5Y 8/1 5Y 8/1 150.5Y 8/ 7.5Y 8/1 7.5Y 8/1.5Y 8/ 7.5Y 8/1 5Y 8/1 180.5Y 8/ 7.5Y 8/1 5Y 8/1.5Y 8/ 7.5Y 8/1 5Y 8/1 10.5Y 8/ 7.5Y 8/1 5Y 8/1.5Y 8/ 7.5Y 8/1 7.5Y 8/1 40.5Y 8/ 5Y 8/1 5Y 8/1.5Y 8/ 7.5Y 8/1 7.5Y 8/1 w w y y» 1.5 wt.% ù w y w. w, x 5 N» w w wš ƒ y ùkþ. y ƒƒ 0.5, 1 N 0.15 M ƒw Fig. 4c w. y 90 w, 1N 10, 0.5N 60 y ƒ d. L- g w ¼ w. L- g w ƒ,» w ù, y w. w,» 1 N w, 1.3wt.% w 0.5 N w 1.4wt.% w. 3.. y z p p y 3..1. y y w y w w p w d w, y y w (Table ). ù k z w w y. 8/1 w ƒ w. d y w s, ƒw Fig. 5. Plots of brightness versus reaction time after treated with different concentration of sulfuric acid(a) and hydrochloric acid(b). Solid triangle; 5N, solid rectangle; N, and solid diamond; 1N. ùkü. 1 N y, 54.7% 66.3% ¼ ƒ w. N y ¼ 61.6% 7.4% ƒ w, 5 N y 64.5% 77.6%¾ ƒ w (Fig. 5a). 5 N y 90, N y 10 70% w

p ü w y L- g e w 147 Table 3. Munsell notations of illite powders after treated with organic acids. process reaction time(min.) 0.15M L-ascorbic acid 0.15M Oxalic acid 30.5Y 8/3.5Y 8/ 60.5Y 8/ 10 YR 8/ 90.5Y 8/ 7.5Y 8/1 10.5Y 8/ 7.5Y 8/1, 1 N y 40 70% w w. w w ùkü, 1 N 5.4-65.8%, N 64.-75.1%, š 5N 73.8-78.1% ƒ w (Fig. 5b). 5 N 30 l s ³ 75% ¾ yƒ w š, N 90 70% w. ù 1 N y 70% w w.» w» w w d w (Table 3, Fig. 6a). L- g w.5y w ùkü. 8 ùkû ù ƒ, w 57.5% û ùkû. w, 8/1 š ¾ w ù w 65.3% w w.» w w û w ùkþ. yw w L- g ƒw y x, w ùkþ, y w yw z ùkþ. Fig. 6b w, y w yw 30 0.5 N, 1 N ƒ 7.1% w d 60 ƒƒ 74.4% 74.3% ùkü. z 10, 73.7% 71.5% w ùkþ, 0.5N 1N j d. L- g yww ƒw ƒ w ƒ w. 1 N w, Fig. 6. Changes in brightness with different set of inorganic and organic acids, and reaction time. (a) Treated with 0.15M L- ascorbic acid(solid circle) and 0.15M oxalic acid(solid triangle), (b) with 0.15M L-ascorbic acid in 0.5N H SO 4 (open circle), 1N H SO 4 (solid circle), 0.5N HCl (open rectangle), and 1N HCl(solid rectangle), and (c) with 0.15M oxalic acid in 0.5N H SO 4 (solid circle), 1N H SO 4 (solid rectangle), 0.5N HCl (solid diamond), and 1N HCl(solid triangle).

148 tá Á Table 4. Munsell notations of illite powders after treated with 0.15M L-ascorbic acid in inorganic acid solutions. process L-ascorbic acid in H SO 4 L-ascorbic acid in HCl reaction time(min.) 0.15M +0.5N 0.15M +1N 0.15M +0.5N 0.15M +1N 30 5Y 8/1 5Y 8/1 7.5Y 8/1 5Y 8/1 60 5Y 8/1 5Y 8/1 5Y 8/1 5Y 8/1 90 5Y 8/1 5Y 8/1 5Y 8/1 5Y 8/1 10 5Y 8/1 5Y 8/1 5Y 8/1 7.5YR 8/1 Table 5. Munsell notations of illite powders after treated with 0.15M oxalic acid in inorganic acid solutions. process Oxalic acid in H SO 4 Oxalic acid in HCl reaction time(min.) 0.15M +0.5N 0.15M +1N 0.15M +0.5N 0.15M +1N 30 7.5Y 8/1.5Y 8/ 7.5Y 8/1 10YR 8/ 60 7.5Y 8/1 7.5Y 8/1 7.5Y 8/1 7.5Y 8/1 90 7.5Y 8/1 7.5Y 8/1 7.5Y 8/1 7.5Y 8/1 10 7.5Y 8/1 7.5Y 8/1 7.5Y 8/1 7.5Y 8/1 Table 6. Mean and 90%-cumulative particle sizes (µm) after treated with CBD and acids. Process Mean (µm) 90%-cumulative (µm) Untreated 8.47 44.35 CBD 8.04 37.84 5 N H SO 4 for 150 min. 7.78 34.04 5 N HCl for 90 min. 7. 31.46 0.5 N H SO 4 for 60 min. + AA 8.60 37.39 1 N HCl for 30 min. + AA 8.55 37.3 0.5 N H SO 4 for 60 min. + OA 8.3 37.41 0.5 N HCl for 90 min. + OA 8.57 34.11 Note: AA: L-ascorbic acid, OA: Oxalic acid. 30 ƒ 71.6% š z 10 64.%¾ w w ùkü. 0.5N w x s w, y w yw ùkù û d. d 1 N 10 ƒ 7.5YR 8/1 d, 5Y 8/1 y ùkü (Table 4). ƒw d, s³ 7.5Y ù, w. x ƒ 8/1 w (Table 5). L- g ƒw û z sw 66.8% w w (Fig. 6c). L- g ƒ y ƒw w j ùkû. ù w y w ùkü p w w. 0.5N y w 65%-66.8%, 1 N y w 63.7%-65.1% d y ƒ ƒw û Fig. 7. Effects of iron removal on particle size distribution of illite samples. H; treated with 5N HCl for 90 min, HA; treated with 0.15M L-ascorbic acid in 1N HCl for 30 min, SA; treated with 0.15M L-ascorbic acid in 0.5N H SO 4 for 60min, S; treated with 5N H SO 4 for 150 min, HO; treated with 0.15M oxalic acid in 0.5N HCl for 90 min, and SO; treated with 0.15M oxalic acid in 0.5N H SO 4 for 60 min. d. ƒ x 0.5N w 64.%-66.1% w 1N

p ü w y L- g e w 149 Table 7. Chemical compositions (wt.%) of illite powders after treated with acids. Composition Untreated S H SA HA SO HO SiO 50.16 51.5 51.33 51.11 51.03 50.34 50.3 Al O 3 31.35 3.05 31.83 3.19 31.99 33.14 33.6 K O 7.96 8.15 8.1 8.14 8.1 8.14 8.15 Fe O 3 * 3.0 1.65 1.6 1.66 1.68 1.67 1.66 Na O 0.71 0.70 0.70 0.71 0.71 0.9 0.84 TiO 0.44 0.45 0.45 0.46 0.45 0.47 0.45 MgO 0.39 0.34 0.33 0.33 0.34 0.30 0.9 P O 5 0.05 0.04 0.04 0.04 0.05 0.04 0.04 CaO 0.09 N.D. N.D. 0.01 0.01 N.D. N.D. MnO 0.01 N.D. N.D. N.D. N.D. N.D. N.D. L.O.I 5.03 4.8 4.79 4.89 4.85 4.95 4.9 Total 99.0 99.71 99. 99.55 99.1 99.97 99.95 *Total Fe calculated as Fe O 3. **H; treated with 5N HCl for 90 min, HA; treated with 0.15 M L-ascorbic acid in 1N HCl for 30 min, SA; treated with 0.15M L-ascorbic acid in 0.5N H SO 4 for 60 min, S; treated with 5N H SO 4 for 150 min, HO; treated with 0.15M oxalic acid in 0.5N HCl for 90 min, and SO; treated with 0.15M oxalic acid in 0.5N H SO 4 for 60 min. Table 8. Iron Extraction Yield (IEY; %) and brightness improvement after treated with CBD and acids at the optimized reaction conditions. Treatment Removed Fe O 3 (wt.%) w 60.1%-65.3% d. 3... s y s š w, trimodal xk ƒ 70 µm ƒ x w (Fig. 7). w w y q. ƒ w w, CBD w (Table 6). w modeƒ, y ƒ w û d š. 3..3. Ÿ yw y X- z, ƒ z Ÿ yƒ w y. k mw y z, p q IEY (%) Brightness (%) Untreated - - 4. - CBD 1.49 49 77.1 34.9 5N H SO 4 for 150 min. 1.51 50 75.1 3.9 5 N HCl for 90 min. 1.63 54 75.1 3.9 0.5 N NH SO 4 for 60 min.+aa 1.43 47 74.4 3. 1 N HCl for 30 min.+aa 1.48 49 71.6 9.4 0.5 N H SO 4 for 60 min.+oa 1.45 48 66.8 4.6 0.5 N HCl for 90 min.+oa 1.44 48 66.1 3.9 Note: Fe O 3 : total iron, AA: L-ascorbic acid, and OA: Oxalic acid. w ƒ w w. Table 7. ƒ w w k 3.0 wt.% w ù ww k z 1.6Ê1.68 wt.% w. w w 45% Fe O 3ƒ w. ü 0.17Ê0.18 wt % q 4% eyw. 3.3.» y z sƒ ƒ k w 3.0wt.% y w y w IEY (Iron Extraction Yield) w (Table 8). ƒ w y w 1.5wt.%, IEY 50% w w. ƒ k IEY 47-54% s w B

150 tá Á Fig. 8. Plots of iron extract yield versus reaction time showing effect of L-ascorbic acid. (a) treated with 0.5N H SO 4 and (b) 0.5N H SO 4 + 0.15M L-ascorbic acid. Fig. 9. Plots of brightness versus reaction time showing effect of L-ascorbic acid on brightness improvement., p t e y w. ù ƒ w» j, p» 10 y w. 5 N y ƒ ƒ w, ƒƒ 90 150 ƒ.»» (L- g, ) ƒw yw w» j k y w. w» z 10 ü ww w y. Fig. 8 9 mw 0.5 N 5 N y ƒƒ w 0.15 M L- g ƒw yw w y w. 0.5 N y w IEY 60 18% 10 7%. ƒ 10, 5 N y w x 60 45% 10 47% j w y w. w IEY s y 0.5N w k 0.15M L- g ƒw yw w. L- g ƒw IEY 46-49%, y 10 w x w ù y z y w. w L- g ƒw yw k w w» w» w z w. ƒ k y, ƒ

p ü w y L- g e w 151 Table 9. Comparison of the optimized reaction condition and results with previous studies. Treatment Material Initial Fe O 3 IEY Brightness (wt.%) (%) (%) Ambikadevi et al. (000) 0.15M OA in 1N H SO 4 at 100 o C for 90 min kaolinite 0.93 66.33 7.89 Veglio et al. (1998) OA 3 kg/t + H SO 4 kg/t at 90 o C for 5 h quartz 0.059 45 - Mandal et al. (004) 0.1M OA for 6h at 80 o C kaolinite 1.87 50 - Cameselle et al. (1997) 7.1 kg/t OA in ph=1.13 at 80 o C, 6 h kaolinite.3 56.5 - This study 0.15M AA in 0.5N H SO 4 at room temp for 60 min. illite 3.0 47 74.4 Note: Fe O 3 : total iron, AA: L-ascorbic acid, and OA: Oxalic acid. š w, ƒ z (0.15 M L- g +0.5 N y )» (Veglio et al., 1998; Cameselle, 1997; Ambikadevi and Lalithambida, 000; Mandal and Banerjee., 004) w (Table 9).» ƒ y w û e ù p w ù, z š, ü w û w ùkü. 4. p K 1.47 Na 0.19 (Al 3.71 Fe 0.18 Mg 0.07 Ti 0.05 )(Si 6.37 Al 1.63 ) O 0 (OH) 4, M 1 x. Ÿ p w 94wt.% ù, Ÿ ü y ty w y xk p t e w 4.% û r. y w» w» (y, ),» (L- g, ), yw (y +L- g ) w w xw. x 0.5 N y 0.15 M L- g ƒw yw k ww, 60 1.5wt% y w ƒ z ùkü. y z p ƒ 4% 75%, ƒ 10YR 8/4 5Y 8/1 w CBD ƒw, p wš y ƒ s ù Ÿ w / Áyw p yƒ. w L- g y ƒ w yw w, y w j j y z w y w. 005 ( ) w w w ( y: KRF-005-041-C00465), w š w w. š x Ambikadevi, V.R. and Lalithambida, M. (000) Effect of organic acids on ferric iron removal from iron-stained kaolinite. Applied Clay Science, 16, 133-145. Cameselle, C., Nunez M.J. and Lema, J.M. (1997) Leaching of kaolin iron oxides with organic acids. J. Chem. Tech. Biotechnol, 70, 349-354. Conley, R.F. and Lloyd, M.K. (1970) Improvement of iron leaching in clays: optimizing processing parameters in sodium dithionite reduction. Ind. Eng. Chem. Process. Des. Develop., 9, 595-601. Grim, R.E., Bray, R.H. and Bradley, W.F. (1937) The mica in argillaceous sediments. American Mineralogist,, 813-89. Mandal, S.K. and Banerjee, P.C. (004) Iron leaching from china clay with oxalic acid: effect of different physicochemical parameters. Int. J. Miner. Process., 74, 63-70. Rieder, M., Cavazzini, G., D'yakonov, Y.S., Frank- Kamenetskii, V.A., Gottardi, G., Guggenhem, S., Koval, P.V., Muller, G., Neiva, A.M.R., Radoslovich, E.W., Robert, J.L., Sassi, F.P., Takeda, H., Weiss, Z. and Wones, D.R. (1998) Nomenclature of the Micas. The Canadian Mineralogist, 36, 41-48. rodo, J. and Eberl, D.D. (1984) Illite: in Micas, Reviews in Mineralogy, 13, S.W. Bailey, ed., Mineral. Soc. Amer., Washington, D.C., 495-544. Veglio, F., Passariello, B., Toro, L. and Marabini, A.M. (1996) Development of a bleaching process for a kaolin of industrial interest by oxalic, ascorbic, and sulfuric acids: preliminary study using statistical methods of experimental design. Ind. Eng. Chem. Res., 35, 1680-1687. Veglio, F., Passariello, B., Barbaro, M., Plescia, P. and Marabini, A.M. (1998) Drum leaching tests in iron removal from quartz using oxalic and sulphuric acids. Int. J. Miner. Process., 54, 183-00. 007 4 š, 007 4 19.