Alkali activation of natural clay using a Ca(OH)₂/Na₂CO₃ alkaline mixture

Abstract

An experimental investigation was conducted on the alkali activation of a kaolinitic clay using an alkaline mixture composed of hydrated lime (Ca(OH)2) and sodium carbonate (Na2CO3) solution. The Ca(OH)2/Na2CO3 alkaline mixture was developed to overcome the high cost and chemical aggression associated with classical alkaline solutions. The mineralogical composition and microstructure of the alkaline mixture and alkali-activation products were studied using X-ray diffraction, attenuated total reflectance-Fourier transform infrared spectroscopy, thermogravimetric analysis and energy-dispersive X-ray-scanning electron microscopy techniques. Pirssonite (Na2Ca(CO3)2·2H2O), calcite (CaCO3), and sodium hydroxide (NaOH) formed as a result of mixing of Ca(OH)2 with Na2CO3. The alkali activation of natural clay with the Ca(OH)2/Na2CO3 alkaline mixture produced a binding agent identified as hydroxysodalite phase (Na8Al6Si6O24(OH)2·4H2O) when pure kaolinite was used, and cancrinite carbonate (Na6Ca1.5[Al6Si6O24](CO3)1.5·1.8H2O) when kaolinitic clay with high a calcite content was used. The mechanical strength of the binder developed was evaluated on cylindrical specimens containing granite waste as a filler material under dry and soaked conditions. The classical NaOH activator was used for comparison. For specimens produced using a Ca(OH)2/Na2CO3 mixture as the alkaline activator, the recorded strength valuewas 21 MPa which was 35% less than that achieved by the classical NaOH solution. Durability tests on samples soaked in water for 24 h showed a reduction in strength from 34 to 22 MPa for specimens prepared with NaOH solution, and from 21 to 11 MPa for the specimens prepared with a Ca(OH)2/Na2CO3 alkaline mixture.

Synthesis of Hydroxy-Sodalite/Cancrinite Zeolites from Calcite-Bearing Kaolin for the Removal of Heavy Metal Ions in Aqueous Media

“…In contrast, zeolite Na-P1, zeolite LTA, sodalite, and analcime result when the concentration of NaOH in the reaction mixture is lower than a molarity of 4 [24,29]. Different cost-effective binary alkaline systems of low causticity have also been developed for the alkali-activation of kaolinite [22,30]. Esaifan et al [22] reported the formation of a kaliophilite zeolite by reacting kaolinite with calcium hydroxide/potassium carbonate (Ca(OH) 2 /K 2 CO 3 ) as the alkaline activating mixture.…”

“…Esaifan et al [22] reported the formation of a kaliophilite zeolite by reacting kaolinite with calcium hydroxide/potassium carbonate (Ca(OH) 2 /K 2 CO 3 ) as the alkaline activating mixture. Shaqour et al [30] also synthesized a cancrinite-type zeolite by activating kaolinite with a calcium hydroxide/sodium carbonate (Ca(OH) 2 /Na 2 CO 3 ) alkaline mixture.…”

Potential use of Kebilian clay reserves(southern Tunisia)for the production of geopolymer materials

“…The most common clay material used for geopolymers is dehydroxylated kaolin, known as metakaolin (Duxson et al , 2007; Hounsi et al , 2013; Shaqour et al , 2017). Less frequently, 2:1 dioctaheral-layer silicates such as illite, smectite or even interstratified illite–smectite may be used for the production of these binders.…”

Decarbonisation of calcium carbonate at atmospheric temperatures and pressures, with simultaneous CO2 capture, through production of sodium carbonate

“…10 Industrially, Na 2 CO 3 is mainly produced through the Solvay process which requires large amount of thermal energy and CaCO 3 calcination. 33 The produced Na 2 CO 3 can have several uses in the industry: (1) for flue gas CO 2 sequestration through the production of NaHCO 3 , 34,35 (2) as an alkali activator for cements, either directly or in the production of activators such as sodium silicates, 36,37 (3) in the production of precipitated calcium carbonate from brine for use as a cement admixture, 38 (4) to regenerate the necessary NaOH, 21,[39][40][41] and/or (5) sold for the manufacture of other commodities (e.g. glass).…”