A Study on Recycling Gypsum

废石膏作为医疗废物处理。我们着眼于石膏遵循可逆反应的事实，并旨在回收使用过的石膏。根据我们的研究，当将硬化的市售半水石膏加热至180 ℃ 210分钟，并粉碎至106 μ m的粒度以用水以0.50的粉/水比研磨时，石膏再次凝固，并产生放热反应的一些热量。在此条件下获得的干压强度平均为84.7 kgf/cm ^2，这是典型的β-半水石膏的干压强度的三分之一或更少。在180 ℃下加热210分钟对于实际的回收应用来说太长，因此，我们将用过的石膏加热到700 ℃的温度，这是普通牙科炉中可用的温度水平。在700 ℃下加热10分钟后的重量损失表明，施加到石膏粉末上的水的重量与施加到石膏粉末上的水的重量大致相同。一 ...更多信息 改进的粉碎方法得到小于45 μ m的颗粒尺寸，并且收集率提高到60%的水平。当将加热和粉碎的再生石膏粉末与水以0.43的粉/水比捏合时，干压强度平均为251.4kgf/cm ^2，这与在180 ℃加热210分钟然后粉碎至106 μ m或更小的粒度的条件下获得的干压强度相比显著高。干压强度值为典型β-半水石膏的干压强度值的约70至80%的水平。研究结果表明，粉磨方法的改进使其颗粒大小接近商品半水石膏，且较低的掺水比使其具有足够的可处理性，从而提高了石膏的干压强度。当300 g *-半水石膏在1600 W的电子烘箱中以70%的功率输出处理10分钟时，所得的质量损失几乎等于用于捏合的添加水的重量。当将石膏粉碎至小于45 μ m的粒度并以粉/水比为0.43与水捏合时，石膏在放热反应中重新凝固。然而，当放置在电烤箱中的石膏量超过300克时，在用水捏合粉碎的石膏粉末后，石膏不能重新凝固，因此，电烤箱不适用于一次回收大量石膏。少

Used gypsum is treated as a medical waste. We focused on the fact that gypsum follows reversible reaction, and aimed to recycle the used gypsum. According to our study, when a hardened commercial *-hemihydrate gypsum was heated to 180ﾟC for 210 minutes, and was pulverized to 106 mum of particle size to knead with water at a powder/water ratio of 0.50, the gypsum set again with some heat generation of exothermic reaction. The dry-compressive strength gained under this condition was 84.7 kgf/cm^2 as average, which was at one third or less of that of typical beta-hemihydrate gypsum.The heating time of 210 minutes at 180ﾟC is too long for practical recycle application, therefore, we heated a used gypsum to a temperature of 700ﾟC which was available temperature level in ordinary dental furnace. The weight change of the used gypsum was measured at every minute.The weight loss after 10 minutes heating at 700ﾟC showed approximatlly the same weight of water applied to knead the gypsum powder. A … More n improved pulverizing method gave less than 45 mum of particle size, and the collecting ratio increased to a level of 60 %. When the heated and pulverized recycled gypsum powder was kneaded with water at a powder/water ratio of 0.43, the dry-compressive strength became 251.4 kgf/cm^2 as average, which was significantly high comparing with that obtained under the condition of heating at 180ﾟC for 210 minutes followed by pulverizing to 106 mum or less of particle size. The value of dry-compressive strength was a level of around 70 to 80 % of that of typical beta-hemihydrate gypsum. Presumable reasons of improved dry-compressive strength are that the improvement of pulverizing method provides nearly equal particle size with that of commercial *-hemihydrate gypsum and that less water mixing ratio provides sufficient treatability.For further shortening the heating time, we tested to apply an electronic oven. When 300 g of *-hemihydrate gypsum was treated in an 1600 W electronic oven with 70 % of power output for 10 min., the resulted mass loss was nearly equal to the added water weight for kneading. When the gypsum was pulverized to less than 45 mum of particle size and was kneaded with water at powder/water ratio of 0.43, the gypsum re-set in exothermic reaction. When, however, the quantitity of gypsum placed in the electronic oven exceed 300 g, it did not re-set after kneading the pulverized gypsum powder with water.Consequently, the use of electronic oven should not be applicable for recycling a large amount of gypsum at a time. Less