The possibility of obtaining beta-anhydrite from waste nitrogypsum

Abstract

The possibility of obtaining β - anhydrite from nitrogypsum, which is waste from a nitrocellulose plant, was investigated. It was shown by means of qualitative IR analysis that the product obtained by heating nitrogypsum for 5 hours at 700 o C was â - anhydrite. When the β- anhydrite was mixed with water at a W/S (water/solid) ratio of 0.54 in presence of different accelerators (CaO, mixture CaO - ash, ash, Na2SO4 and K2SO4), pastes were formed which hardened on standing. The compressive strength of the hardened samples was measured after 7 and 28 days and their composition determined by qualitative IR analysis. On the basis of these results, it was observed that a relationship exists between the composition (depending on the used accelerator) and the compression strength of the samples. Namely, the formation of large cores of double salts: syngenite (K2SO4 ⋅CaSO4 ⋅H2O) and glauberite (Na2SO4 ⋅CaSO4), in the presence of the accelerators K2SO4 and Na2SO4, respectively, was due to the rapid and complete crystallization of the dihydrate (CaSO4 ⋅2H2O). This fast crystal growth of the dihydrate resulted in high compressive strengths of these samples. In the other samples (prepared in presence of the accelerators: CaO, mixture CaO - ash and ash), dihydrate did not form and, consequently, their compressive strength was low

Influence of the setting activators on the physical mechanical properties of phosphoanhydrite

“…Based on the data from the literature [18] it can be stated that the crystals of glauberite and syngenite with large specific surfaces act as crystallization centers predetermining rapid hydration. After 1 day of phosphoanhydrite hydration with K 2 SO 4 additive, syngenite forms with the following absorption bands: 1195, 1130, 750, 645, 608 ( Figure 6, curve 5); and upon using Na 2 SO 4 additive, glauberite forms -635, 610 ( Figure 6, curve 6) [13,19]. The spectra of phosphoanhydrite calcined at 800 and 900 °C with and without Na 2 SO 4 and K 2 SO 4 additives after 2 h and 1 day are similar.…”

“…Activation of anhydrite cement can be increased upon grinding it with impurities [3,10,11] or dissolving activators in water during specimen formation [4,5,12,13]. Different researches analysed the impact of the following hardening activators: Na 2 SO 4 , K 2 SO 4 , (NH 4 ) 2 SO 4 , FeSO 4 , CaCl 2 and K 2 Cr 2 O 7 [3][4][5][6][12][13][14][15][16].…”

Preparation and properties of carboxylated styrene‐butadiene rubber/flue gas desulfurization ash composites by in situ carboxylate reaction

“…To address this issue, great efforts have been made by many researchers. FGD has been used in the field of road engineering and building materials, such as aerated concrete blocks, fine slag powder, waterproof roll materials, and asphalt mixtures 3,6,12–18 . Lei et al 19 introduced untreated FGD gypsum‐based high‐strength building materials with good mechanical properties, water resistance, a high hydration degree, and a dense microstructure.…”

Solubility and Phase Transitions of Calcium Sulfate in KCl Solutions between 85 and 100 °C

“…), insoluble AH can be activated and used as a binder (AH cement) in the building industry. 3 Therefore, it also represents very important construction material.…”

“…In the presence of certain accelerators (Na 2 SO 4 , K 2 SO 4 , CuSO 4 , CaO, ash, etc. ), insoluble AH can be activated and used as a binder (AH cement) in the building industry . Therefore, it also represents very important construction material.…”