Luciano Santoro

Hydration of mixtures containing fly-ash, lime and phosphogypsum

Abstract The behaviour of the system fly-ash-lime-phosphogypsum-water has been studied at 25 and 40°C and in the range of composition up to 30 parts of phosphogypsum per 100 parts of a 60 40 mixture of fly-ash and lime. When compared to pure gypsum, phosphogypsum appears to be equally or more effective. Varying the ratio gypsum/fly-ash varies the ratio with which the two major hydration products, calcium silicate and trisulphoaluminate hydrates, are formed. This is important as far as durability and mechanical strength development are concerned.

High-temperature synthesis of calcium sulphoaluminate from phosphogypsum

Abstract The possibility of using phosphogypsum for the production of cements based on calcium sulphoaluminate (3CaO·3Al 2 O 3 ·CaSO 4 ), which is of interest in the fields of rapid-hardening, expansive and energy-saving hydraulic binders, has been examined. Mixtures of CaCO 3 , Al 2 O 3 and phospho- or pure gypsum have been fired at temperatures between 950 and 1350°C for 30 min to 10 h. When compared to pure gypsum, phosphogypsum greatly reduces both the temperature and time required for completion of the synthesis, owing to the fluxing and mineralizing properties of its impurities. The results show that an interesting method of disposal of phosphogypsum can be proposed.

Hydration of granulated blast-furnace slag in the presence of phosphogypsum

Abstract The behaviour of the system granulated blast-furnace slag—phosphogypsum—water has been studied in the presence of a small amount of hydrated lime and in the range of phosphogypsum/slag composition ratio up to 20/100. When compared to pure gypsum, phosphogypsum appears to be a more efficacious activating agent with regard to the formation of the hydrated phases, specifically calcium silicate hydrate and calcium trisulphoaluminate hydrate. The results are worthy of consideration as far as the disposal of phosphogypsum is concerned.

Application of differential scanning calorimetry to the study of the system phosphogypsum—lime—aluminiumhydroxide—water

Abstract The formation of calcium sulphoaluminate hydrates by hydrothermal reactions among phosphogypsum, lime and aluminium hydroxide has been studied in order to evaluate the possibility of disposal of phosphogypsum by conversion into products useful as building materials. The investigation has been carried out with the aid of differential scanning calorimetry as the chief experimental technique. Reaction products in different experimental conditions have been identified and quantitative data have been obtained in order to define optimum conditions with regard to both consumption of phosphogypsum and yield of calcium sulphoaluminate hydrates.

Role of phosphogypsum in the hydration of calcium sulphoaluminate

Abstract In view of possible ways of disposal of phosphogypsum the hydration of a series of preparations of calcium sulphoaluminate, made from this by-product at 1000 and 1100° C or from pure gypsum at 1200 and 1350 ° C, has been studied in mixtures with phospho- or pure gypsum and Ca(OH) 2. The compositions of the mixtures to be hydrated were stoichiometric for the formation of calcium tri- and monosulphoaluminate hydrates. The hydration properties of calcium sulphoaluminate are not significantly influenced by the nature of gypsum employed in the high temperature synthesis. Phosphogypsum impurities act as catalysts in the formation of calcium trisulphoaluminate hydrate which is of major interest among the hydration products of a wide range of cements.

The influence of heavy metals on the hydration of binders of interest for chemical gypsum stabilisation

Abstract The effects of the presence of some heavy metals on the hydration processes of binders useful for waste stabilisation have been investigated. The specific types of waste to which our attention has been directed are the chemical gypsums formed as by-products in a number of industrial processes. Experiments have been carried out with hydratory model systems containing a binder (blast-furnace slag or fly ash-lime mixture), pure gypsum and a heavy metal compound (Cr(OH) 3 , K 2 CrO 4 , Mn(OH) 3 , Fe(OH) 3 , Ni(OH) 2 , Cu(OH) 2 , Cd(OH) 2 or Zn(OH) 2 ). The results have shown that in most cases the hydration processes are substantially unchanged or even favourably influenced. Retarding effects were only observed in the presence of Zn and (to a lesser extent) Cu.