| 摘要 |
PROBLEM TO BE SOLVED: To convert an iron chloride soln. into a high quality useful material at a low cost by obtaining a yellow iron oxide pigment having specified lightness and specified Mn, Cl and Cr contents by a precipitation method using iron (II) chloride and an alkali component. SOLUTION: The yellow iron oxide pigment has full-shade CIELAB unit lightness L* 62.0-64.0, a* 8.5-10.5 and b* 48.5-50.0, has lightness L* 81.6-82.5, a* 3.8-4.8 and b* 37.5-39.5 when it is whitened and contains 0.05-0.055 wt.% Mn, 0.05-0.3 wt.% Cl and <40 mg/kg Cr. An acidic FeCl2 soln. having 50-450 g/l concn. is adjusted to pH3-5 by adding an alkali component, the resultant soln. is added to a suspension ofα- orβ-FeOOH seed crystals by an amt. equivalent to 4-8 times calculated as iron content (mol) and they are mixed at 30-95 deg.C and adjusted to pH 3-5. An oxidizing agent is added by such an amt. as to oxidize 0.5-10 mol.% Fe per 1 hr. Oxidation is stopped at the time when the Fe (II) content is reduced to <1 mol.% and the formed precipitate is separated, dried and comminuted to obtain the objective yellow iron oxide pigment.
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