# Knowledge base: Warsaw University of Technology

Back

## Fabrication of ceramic aggregate based on phosphogypsum and power plant ashes – preliminary studies

### Paulina Urbańska

#### Abstract

Orthophosphoric acid is an important half-product in the production of phosphoric fertilizer. One of the method of the production of orthophosphoric acid is called “wet process”. This method has extremely substantial disadvantage which is creating hefty amount of chemical waste – phosphogypsum (PG). For every ton of orthophosphoric acid made, approximately five ton of phosphogypsum are created. PG is mainly composed of calcium sulphate dihydrate (gypsum) which is 94 –96% by weight. Due to hydronium ions, PG is considered to be acidic. It also contains trace metals and radionuclides. Mostly because of its composition, worldwide utilization of PG is estimated to be around 3 – 5%. The rest of PG is disposed of in stockpiles. The largest stockpile in Poland containing 85 million tons of waste is in Police. Power plant ashes are the next thoroughly gathered waste and because of the fact that national generation of the electricity is mainly based on a combustion of fossil fuels in 2010 agglomeration of fly ash in stockpiles reached 18,5 million tons and 253,7 million tons of dust – slag compounds. Main components are SiO2 and Al2O3 which provide essential pozzolanic properties in terms of using ashes in new applications and many more mineral components. As well as PG, power plant ashes contain trace metals and radionuclides. In the last year in the Department of Inorganic Technology and Ceramics of Warsaw University of Technology the research on the fabrication of lightweight sintered aggregate was successfully finished and the technology is being completed. Upon this success it has 52 been decided to go further and attempt to fabricate ceramic aggregate based on phosphogypsum. Results and discussion The purpose of these studies was to prepare two compositions of fly ash and phosphogypsum. The content of PG was 95 and 50% by weight and fly ash 5 and 50% by weight respectively. The mixtures were subjected to thermogravimetric and differential thermal analyses coupled with quadruple mass spectrometer (TG-QMS). After the agglomeration with water as a binder the granules were obtained. Next step was a sintering process of the granules in the atmosphere of air in the muffle furnace. The temperatures of sintering were 1050, 1100 and 1130°C, the time of sintering were one or two hours and the rate of temperature were 7°C or 8°C per minute. Received aggregate was examined concerning compression strength, porosity and absorption of water. All the results were compared with the results obtained for commercial lightweight aggregate made of ash. It was also determined phase and quantitative composition of aggregate by X – ray Powder Diffraction (PXRD). Thermogravimetric and differential thermal analyses showed that above 1200°C SO2 and CO2 start to emit while there was no emission of fluorine or its oxide. The agglomeration of compositions run easily and as a result granules of good mechanical strength were obtained what has favorable influence on further processes and the need of transportation of granules as well. Higher temperatures of sintering, a longer time of sintering and reducing the rate of temperature have beneficial impact on the quality of obtained aggregate. PXRD showed that the aggregate with 95% by weight content of PG contain no amorphous phase and fluorine appears in carbonate hydroxyl fluorapatite. Conclusions The best parameters of sintering were: the temperature of sintering of the order of 1130°C, two hours time of sintering and the rate of sintering of the order of 7°C per minute. As a result of sintering under such conditions it was possible to obtain aggregate which had higher mechanical strength and comparable porosity and absorption of water in relation to commercial aggregate from ash. On further research it is necessary to investigate the leachability of fluorine from 95-5 aggregate to check if it is possible to use in the production of concrete and also to measure the emission stream of SO2 during the sintering. 53 The fundamental aim of these preliminary studies was to settle the question if there is possibility to utilize phosphogypsum by using it in the production of lightweight aggregate and on the basis of obtained results it can be ascertained that there is.
Record ID
WUT6faa0a645c2b450f85924c5a9b5a1528
Diploma type
Master of Science
Author
Paulina Urbańska Paulina Urbańska,, Undefined Affiliation
Title in Polish
Otrzymywanie kruszywa ceramicznego z fosfogipsu i popiołów elektrownianych – badania wstępne
Supervisor
Janusz Sokołowski (FC/CChT) Janusz Sokołowski,, Chair of Chemical Technology (FC/CChT)Faculty of Chemistry (FC)
Certifying unit
Faculty of Chemistry (FC)
Affiliation unit
Chair of Chemical Technology (FC/CChT)
Study subject / specialization
, Technologia Chemiczna
Language
(pl) Polish
Status
Finished
Defense Date
19-06-2012
Issue date (year)
2012
Keywords in Polish
-
Keywords in English
-
Abstract in Polish
urn:pw-repo:WUT6faa0a645c2b450f85924c5a9b5a1528