Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-07
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • br Materials and methods br Results and discussion br Conclu

    2021-04-19


    Materials and methods
    Results and discussion
    Conclusions The current research work deals with preparation of CES from RHA and comparative study of Ni (II) ion adsorption on CES and RHA. It was observed that carbon embedded silica shows more porous structure and more surface area as compared to the parent compound consequently having a very high adsorption capacity as compared to RHA sample. Different parameters like Adsorbent dosage, Initial pH of Ni (II) ion solution, time of shaking, initial ion concentration, temperature of shaking were varied and the effects were evaluated:
    Acknowledgements
    Introduction The search for alternative binders to reduce greenhouse gas emissions and high demand for energy by the Portland cement industry has gained great concern by the research flt3 [1]. Geopolymers can be a promising alternative binder. These materials are originated from inorganic poly-condensation, the so called “geo-polymerization” and can gain reasonable strength in a short time under adequate curing at temperatures between 20 and 80 °C with 60 °C being the optimum curing temperature for fly ash-based geopolymers [2], [3]. Unlike ordinary Portland or pozzolanic cements, geopolymers do not need calcium silicate hydrates for strength gain but utilize the polymerization of silica and alumina precursor (e.g from metakaolin, fly ash and slag) and a solution of alkali-salts, generally consisting of a mix of sodium hydroxide and sodium silicate or potassium hydroxide and potassium silicate to attain structural strength [4], [5], [6]. The result is a mixture of gels and crystalline compounds that eventually harden into new strong compounds. Alkali activation of aluminosilicate materials that leads to geopolymers represents a complex process that is not yet fully described [7], [8], [9], [10]. In the reaction, the strong alkaline solution breaks the Si-O-Si bonds of the aluminosilicate and new phases are formed by the penetration of Al atoms into the original Si-O-Si structure. These phases are mostly aluminosilicate gels or zeolite precursors. Their compositions are characterized by the formula Mn[-(Si-O)z-Al-O]n·wH2O, where M can be K, Na or Ca atom, n the degree of polycondensation, z is 1, 2 or 3 and w the binding water amount. In diluted suspensions (w > 1), mostly crystalline zeolite type products like analcime and hydro-sodalite are formed. For higher concentration of the solid phase in the suspension (w < 1), amorphous products as poly-sialates depending on the Si/Al ratio are predominant. The network is formed by SiO4− and AlO4− tetrahedrons linked by oxygen bridges. Chains or rings united by Si-O-Al bridges are then formed. The negative charge of Al atom that is present in the coordination 4 is compensated by positive Na+, K+ or Ca2+ ions. Based on their monomeric units, three different inorganic polymers can be distinguished: poly-sialate (PS) (-Si-O-Al-O-) with Si/Al = 1; poly-sialatesiloxo (PSS) (-Si-O-Al-O-Si-O-) with Si/Al = 2 and poly-sialatedisiloxo (PSDS) (-Si-O-Al-O-Si-O-Si-O-) with Si/Al = 3. Metakaolin is the product of calcination of kaolinite rich clay at temperatures between 600 and 850 °C [11], [12] depending on the purity and the crystallinity of the initial clay. The geopolymers from metakaolin as aluminosilicate source have shown promising results in previous works [13], [14], [15] but they have not been considered as effective alternative binders to Portland cement. Less workability and brittleness due to high water demand, shrinkage and cracking during the drying process were pointed as problems affecting the use of metakaolin geopolymers [14], [16]. New methods of elaborating geopolymers using Rice Husk Ash were proposed in the literature. Kusbiantoro et al. [17] studied compressive strength of microwave incinerated RHA and fly ash geopolymer. He et al. [18] characterized red mud/RHA husk ash based geopolymers. In both studies a mixture of sodium silicate and sodium hydroxide was used as alkaline solution. Developments in the fabrication of pure silica from RHA have shown that sodium silicate can be obtained in the process [19], [20], [21], [22], [23]. RHA has also been shown as a promising Supplementary Cementing Material (SCM) in concrete or as pozzolanic materials with hydrated lime due to its high reactivity [24], [25], [26]. Bouzon et al. [27] observed similarity in strength when they used a suspension of RHA/NaOH heated in a reflux system as an alternative commercial water glass (sodium silicate) for fluid catalytic cracking (FCC) for geopolymer design. Tchakouté et al. [28] and Kamseu et al. [29] recently used RHA to produce geopolymers from metakaolin and RHA, but their focus was to synthetize sodium silicate using RHA. Little attention was given to partial substitution of metakaolin by RHA in the solid mix before reacting it with the sodium hydroxide solution.