It has recently become necessary to develop a new process for recovery of phosphorus component from the incineration ash of sewage sludge which is becoming difficult to be disposed. The condition of leaching process was investigated, because the leaching process of phosphoric acid was one of the most important process in recycling the incineration ash. The results can be summarized as follows : 1) Sulfuric acid solution was preferred to sodium hydroxide solution for leaching of phosphorus ions from incineration ash of sewage sludge. It should be paid attention that for leaching process, (1) sulfuric acid concentration is comparatively high, (2) ratio of solid to solution is low, (3) processing temperature makes it high, (4) the leaching rate was fast and leaching time less than 30 minutes 2) The phosphorus component in incineration ash of sewage sludge is existing as calcium phosphate, mainly. It was found that it was possible to prevent from substantial decline by making the ratio of solid to solution comparatively high to control the concentration of Ca2+ ion. 3) The residue after leaching treatment with sulfuric acid solution was not suited to the cement resources, because it included calcium sulfate. By washing treatment with sodium hydroxide, the quantity of SO3 in the residue was reduced and the residue is possible to be utilized as cement resources.
Ammonium polyphosphate (APP) form V was prepared by heating process from the system of ammonium orthophosphate-urea. APP form V with a high purity was obtained by controlling the partial pressure of ammonia gas and humidity in the atmosphere of the reaction furnace. The form V APP was hardly soluble in water and had a very small average particle size of about 3-4μm and can be employed as an useful flame retardant for organic materials.
An effluent standard is becoming severe from a viewpoint of environmental conservation in recent years. Perceiving to reduce selenium (Se (VI)) that it is said to be difficulty, the examination was conducted for removal of selenium in solution with the high concentration of chloride ions which made the removal more difficult. Moreover, the experiment was carried out to remove selenium and fluorine which behaved as anion. The results can be summarized as follows : 1) SeO32- (IV) ions could be removed easily even in the solution with the high concentration of chloride ions. In the case of SeO42- (VI), it was needed to be reduced to SeO32-. The quantity of reducing agent for solution including much amount of chloride ions was required as much as thousand times of amount of SeO42-.2) FeSO4·7H2O was desirable for a reducing agent for the solution of high chloride concentration. FeCl3 was needed to decrease the concentration of Fe. Furthermore, Ca (OH) 2 was suited to adjust pH rather than NaOH. Ca (OH) 2 improved the efficiency of both filtration and removal of SeO42-. 3) It was possible to remove fluorine by using H3PO4 and to remove selenium with FeSO4 continuously. Furthermore, the reaction of both was carried out under the same condition, pH 10. Therefore, it was found that it is an easy processing method to control pH.
A mixed-transitional metal phosphate fluoride containing iron and cobalt in a 1 : 1 ratio, FeCo (PO4) F, has been synthesized by hydrothermal means and structurally characterized via single crystal X-ray diffraction. Along the c axis of the structure, corner-sharing Fe (1) O4F and Fe (2) O4F trigonal bipyramids link via oxygen bridges to form chains, while Co (1) O4F2 octahedra and Co (2) O4F trigonal bipyramids connect each other to form chains by sharing the common edge of O…F and the corner of O alternately. The chains of Fe and Co coordination polyhedra are further connected via oxygen and fluorine bridges, as well as phosphate groups to give a three-dimensional framework structure.
A new observation technique for porous material was developed and applied to examine internal structure of set plaster of gypsum. Three kinds of gypsum with different ratio of water to plaster were examined using confocal laser scanning microscope.The image obtained by the new method directly gave the internal pore structure with high resolution. It provided more information compared with other characterization methods such as immersion liquid method, scanning electron microscopy and mercury penetration.