Encapsulamento cerâmico de resíduos de materiais refratários

Abstract

Ceramic encapsulation for refractory material residues has been studied by a chemically bonded ceramic technique, using a new binder system based on special potassium and magnesium phosphate. Comparison among this technique and conventional fusing andsintering ones, as well, with the chemically bonded ceramics based on hydraulic cements and conventional phosphates has been made.Residues from the most important refractory classes have been used: fireclay and high alumina bricks, high alumina castable, magnesia, chrome-magnesia and MgO-C bricks. Potassium phosphate monobasic (KH2PO4) has been used as a binder and magnesium oxide as reaction activator. The various mixes have been molded by vibration, using asimilar process to concretes. The main characteristics tested have been setting time, reaction temperature evolution, mechanical strength development with curing time, and development of mineralogical phases and microstructure. Many of the common properties to the refractory technology have also been studied. Results have shown to be possible the treatment of refractory residues using this technique of ceramic encapsulation by a potassium and magnesium phosphate bindingsystem. This process shows as advantages to the fusing and sintering ones, a lower operational cost, a lower installation investment and the possibility of residue treatment close to the place where it is generated. In comparison to the hydraulic cement system it shows, as advantage, a higher mechanical strength and a less permeable and soluble structure.Setting retarder addition to the mixes has been important to control the exothermic reaction between potassium phosphate and magnesium oxide, becoming possible to treat large amount of materials by this process. Therefore, setting time is possible to be controlled to a desired level, necessary to handle the mix during its application. The mechanical strength developed by this ceramic, with cold crushing strength above40MPa after 24h of curing, allows its use in a great variety of applications. The development of high mechanical strength in a short period of curing becomes possible some uses where conventional binders have limitation. The hydraulic cement system also has shown good physical and mechanical properties. This system shows worse solubility and leaching test results and may be applied only to ceramic encapsulation for non dangerous refractory residues, inert or non inert. The system based on potassium and magnesium phosphate as a binder may be used to encapsulate dangerous refractory residues, although additional solubility and leaching tests need to be done always a new residue is studied.