| Pyrite cinders is a solid cinder produced by sulfuric acid industry.The comprehensive utilization can not only reclaim the resources but also reduce pollution on environment.Iron oxide pigments have been made from high quality FeSO4.7H2O .it develop the new way to comprehensive utilization of the cinders.The difference from the traditional technology which used acid method to prepare ferric yellow pigments,we use NH3-H2O as precipitating agent replacing NaOH to prepare a -FeOOH seed, and in secondary oxidation iron sheet is replaced by dripping NH3-H2O and FeSO4 solution. Despite NH3-H2O is consumed in chemical reaction,(NH4)2SO4 can be directly reclaimed for the chemical fertilizer or ammonia,and ammonia can be recycled as precipitating agent .Thus the resources are utilized reasonably.The seed preparation is a key step in ferric yellow production.In this phase the formation ,variation, physical phase, size and morphology of a -FeOOH seed are studied by using NH3-H2O as precipitating agent. The effect of initial [Fe +] concentration, air-flow and alkali ratio on seed formation are discussed. The results show that it is almost linear relation between time and Fe2+ conversion accordingly to kinetics feature of zero order reaction. The ferric yellow seed which is yellow, very fine, uniform and needlelike can be gained under following conditions(temperarure: room temperature;air-flow:0.1M3/h(300ml solution);alkali ratio:0. 25 ; initial Fe2+concentration: 30 %). The color of seed continuously changes with time from pearl blue to ultramarine to pitch-black tokelly to yellow. In the process the seed color is changed from pearl blue to ultramarine to pitch-black to kelly and lastly to yellow.In secondary oxidation the effect of Fe2+ concentration,air-flow,seed ratio, pH value,oxidation temperature etc on ferric yellow formation are discussed. From the experiment we draw the best oxidation conditions (Fe2+concentration:0.18-0.25mol/L,air-flow:0.35~0.50M3/ h(1000ml solution), seed ratio:33%, pH value of solution: 2.5~3.5, oxidation temperature:85℃). Physical phase of ferric yellow is a -FeOOH(acicular structure) and all properties of ferric yellow we have determined is reached first grade standard.The technology of preparing ferric red by calcining ferric yellow arereviewed,and the effect of calcining temperature on color and morphology of ferric red are studied. The experiment results show that with calcining temperature rise the color of ferric red gradually deepened from mauve to chrysoidine ,morphology of ferric red also changed.In order to keep acicular structure of ferric red the calcining temperature can not exceed 600 ℃ .It is suitable for ferric yellow to calcine two hours in 500℃.Technology conditions of reclaiming (NH4)2SO4 or ammonia in ferric yellow solution are explored. The experiment results show that GB535-83 industry grade standard of (NH4)2SO4 crystal can be attained by first using H2O2 oxidation and then adjusting pH value to 4.7~5.5 . The recovery ratio of ammonia can reach 94.5 % when calcium oxide is added to ferric yellow solution using low pressure distillation in 95 ℃. |
