Using phosphor-gypsum (PG) to produce sulfuric acid is one of the most effective ways of recycling sulfur resources. This paper studied the melting and decomposition behavior of PG with High Temperature Microscope and Infrared Sulfur Analyzer. Moreover, a new process of PG decomposition for producing sulfuric acid and lime is proposed and discussed. The result shows that the minimum communion point of PG is higher than 1200 °C, the desulphurization degree of PG at 1200 °C under reducing-oxidizing atmosphere can exceed 90%, and the decomposition products of PG have high hydration activity. This means that little liquid phase will occur if PG is decomposed at1200°C, so PG can be decomposed using a fluidizing furnace. The new process of PG decomposition for producing sulfuric acid and lime has many advantages over the traditional process of PG decomposition for producing sulfuric acid and cement, and has a broad application prospects.
Contamination of aggregates with gypsum occurs frequently. Fine aggregate has more detrimental effect due to its large surface area. An experimental work had carried out to investigate the behavior of mortar made from six SO3 contents in the fine aggregate, five size fractions of gypseous aggregate and three C¬3A contents in the cement. The results show that significant expansions do not occur within mortar bars if the content of SO3 lies below 1.25% by the weight of fine aggregate and the reduction in strength is higher in later ages and for higher SO3 contents. The size fraction of gypseous aggregate also affects the degree of expansion, especially in the case of fine particles. The cement with C3A content lower than 5% can tolerate a higher level of contaminant gypsum.
To produce 130MPa reactive powder concrete with iron tailing sands as aggregation in an economic hot curing system, the effects of curing temperature, curing time and curing conditions on the reactive powder concrete was studied, the reasons of the strength of reactive powder concrete in different curing systems has the difference from the submicroscopic structure point of view was analyzed. The results show that use 90°C hot water to cure reactive powder concrete for 48h can lead it’s 28 day compressive strength reaches 140MPa, the flexural strength reaches 28MPa.
In this paper, an Infrared Sulfur Analyzer is set to measure the desulphurization degree during thermal decomposition of phosphor-gypsum, which provides a much quick, convenient, continuous and accurate method. It might be considered as an effective way to study kinetics of phosphor-gypsum (or phosphogypsum) thermal decomposition (or pyrolysis). With the help of this method, the desulphurization degree and desulphurization rate of broadly constituted phosphor-gypsum samples in the temperature range of 1250-1400°C were studied. The experimental results show that the desulphurization degree increase with the rising of temperature in the range of 1250-1300°C quickly, however, this increase is not obvious when the temperature is above 1300°C. Besides, the corresponding regression equations are obtained. The decomposition degree of phosphor-gypsum could be judged according to the regression equations mentioned above.
The effectiveness of fly ash in suppressing expansion due to alkali-silica reaction (ASR) of sandstone are studied respectively based on accelerated mortar bar test and concrete prism test. The mechanism of fly ash in inhibiting the ASR of sandstone is examined by scanning electron microscope (SEM) and energy dispersive analysis of x-ray (EDAX). Moreover, the reliability of fly ash in inhibiting ASR of sandstone was discussed through concrete strength and frost resistance tests. Results indicate that the replacement amount of fly ash is 20%, the expansion due to ASR can be decreased to the critical value of a non-reactive aggregate. The reason why fly ash can inhibit the alkali reactivity for the sandstone is that the strong reaction between alkali and fly ash dissipates the alkali, and the products of alkali-silica-aluminate gels are non-expansible. For the concrete specimens suffered from accelerated ASR tests, their strength and frost resistance are decreased with the increment of fly ash replacement.
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