การเตรียมแอลฟาปลาสเตอร์จากฟอสโฟยิปซัม

Preparation of a-Plaster from Phosphogypsum

Name: ภาณุมาศ ไชยสมบูรณ์

Organization : มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

Name: Panumat Chaisomboon

keyword: Phosphogypsum

; Hemihydrate Calcium Sulfate

; Plaster

; Radioactivity

; Dehydration

; Rate

; Normal Consistency

; Setting Time

; Compressive Strength

Abstract: This special research project aims to investigate the possibility of preparing -plaster from phosphogypsum by the wet calcination process. Moreover, the studying of the effect of radioactive elements and phosphorus pentoxide (P2O5) in phosphogypsum on the physical properties of the obtained -plaster, and also the effect of calcium chloride concentration on the dehydration rate of phosphogypsum are focused, too. The gypsum samples used in this research were divided into 3 groups which are natural gypsum, unpurified phosphogypsum from NFC and purified phosphogypsum from NFC. The 4 percent aqueous citric acid solution was used to purify phosphogypsum to produce the third group of gypsum sample. Each batch of sample was boiled in calcium chloride solution, at different concentrations (2M, 3M and 4M of CaCl2) at 105 oC and 220 rpm of stir speed. It was found that the impurities in the unpurified phosphogypsum especially P2O5, and F are reduced in the 4 percent of citric acid solution and water washing. In addition, the salt concentration directly affects the dehydration rate of all gypsum groups. The high CaCl2 concentration results in the faster dehydration rates than at low CaCl2 concentration. The pH values of the obtained -plasters from all raw material groups are close to the neutral point. The Ra226 found in the obtained -plasters from phosphogypsum are reduced from 672.86 Bq/kgdry to 75.58 Bq/kgdry (88.77 percent reduction) after the calcination of unpurified phosphogypsum and also reduced from 832.33 Bq/kgdry to 89.17 Bq/kgdry (89.29 percent reduction) after the calcination of purified phosphogypsum. The activity concentrations of Ra226 of plasters which obtained from both phosphogypsum are lower than 370 Bq/kgdry, which is the limitation of Ra226 in gypsum sample that the Office of Atomic Energy for Peace or OAEP recommends. It is also shown that there is a high possibility to produce the -plaster from purified phosphogypsum because the obtained -plaster from the optimal conditions which is the calcination of purified phosphogypsum in 2M of CaCl2 for 2.5 hr has a neutral pH value (6.66 at 60 percent by weight), the lower of activity concentration of radioactive elements (111.82 Bq/kgdry) than the exemption level, and moderate compressive strength (11.03 MPa which higher than that from natural gypsum, 8.35 MPa) but still high consistency and setting time (57.5 ml per 100 grams of plaster, and 20.63 minutes, respectively)which need to be studied further of how to improve these properties of the obtained plaster. However, the compressive strength of -plaster from the calcination of purified phosphogypsum in 2M of CaCl2 for 2.5 hr is 60.42 percent lower than that of commercial -plaster (27.86 MPa) may be because of the two reasons. Firstly, the impurities still remain in the obtained -plaster, and secondly, the wet calcination process produces the rod shaped crystal of -plaster and some Cl- contaminates in the obtained plaster which possibly affect the increasing of the normal consistency and the decreasing of compressive strength of the obtained plasters.

มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี

Address: กรุงเทพมหานคร (Bangkok)

Email: info.lib@mail.kmutt.ac.th

Name: Lect. Jindarat Pimsamarn

Role: Supervisor

Created: 2546

Issued: 2005-09-19

Modified: 2006-05-09

วิทยานิพนธ์/Thesis

ISBN: 9744564075

CallNumber: CHE1407

tha

DegreeName: Master of Engineering

Level: Master's Degree

Descipline: Chemical Engineering

Grantor: King Mongkut's University of Technology Thonburi

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