Solidification Versus Adsorption for Immobilization of Pollutants in Geopolymeric Materials: A Review

Geopolymer (GP) is a class of three-dimensional aluminosilicate binder, which is superior to Portland cement materials in acid, heat and fire resistance. GP is produced by reacting an aluminosilicate source (metakaolin, fly ash or waste) with an alkali metal hydroxide or silicate. The aim of the present work is to review the latest developments in three lines of research that deal with application of GP in treatment of pollutants. The first “intra-solidification” that involves mixing real waste (containing heavy metal pollutants) with the GP precursors to obtain a high mechanical strength material. The second type of solidification is “inter-solidification” that involves incorporation of heavy metals solutions (as simulation of polluted water) during geopolymerization reaction. The third line of research “adsorption” involves agitating GP with heavy metals solutions and studying the ability of GP to remove heavy metals from water. These techniques will be investigated regarding efficiency and mechanism of immobilization, cost and environmental impact. GPs are strong low-cost adsorbents for heavy metals. In intra-solidification, despite the high mechanical strength of the produced GP-containing waste, geopolymerization reduces effectively the leaching of heavy metals. The reverse was observed in the case of inter-solidification which presents a greater challenge than intra-solidification

Development of functional geopolymers for water purification, and construction purposes

This paper deals with the development of functional geopolymers based on local resources such as kaolinitic soil and zeolitic tuff for the construction of water storage containers and water transfer channels. The effect of water content on the mechanical performance and physical properties of synthesized geopolymers was evaluated. The results confirmed that the optimum ratio of water is 28% of clay fraction, which revealed observable improvements of physical, mechanical, and adsorption properties of the geopolymeric products. Such geopolymers showed the highest compressive strength, density, and maximum adsorption capacity toward cadmium among the products and precursors tested. The residual soluble salts in produced geopolymers were markedly reduced by using this optimum water content

Blending Plastics Waste with Highly Available Jordanian Kaolin for Preparation of Alkali-Activated Mortars

Due to their lower energy demand, alkali-activated materials or geopolymers (GPs) are strong candidates to replace ordinary Portland cement binders in some applications. The present article attempts to investigate the possibility of incorporating plastics waste in place of silica sand filler in the GP mortars. The compressive strength, density, FTIR, XRD, BET and SEM of the prepared mortars were evaluated. Satisfactory compressive strength was achieved for metakaolin (MK)-based GP mortars containing plastic fillers (polyvinylchloride (PV), polystyrene (PS), polypropylene (PP) and polyethylene (PE)) which was dependent on the nature of plastic incorporated in the GP matrix: MKPV (30.3 MPa) > MKPS (15.8 MPa)~MKPP (15.9 MPa) > MKPE (9.1 MPa). The 28-day compressive strength of GP containing polyvinyl chloride was almost equivalent to that containing silica sand. Much lower values were obtained for the corresponding kaolin-based GPs (2.5, 2.8, 1.8 and 2.2 MPa, respectively). As reflected by FTIR absorption bands at 1447 and 1400 cm−1, the addition of plastic filler reduces absorption of CO2 from the atmosphere which enhanced dissolution of Al species from metakaolin. The morphology of GPs containing plastic fillers exhibited amorphous tissue-like structure compared to crystalline structure in the case of GP containing silica sand. However, both types of GPs exhibited lower porosity than previously prepared metakaolin-based GPs. Remarkably, poor adhesion of plastic filler to the GP binder was observed due to the inertness of plastic fillers toward alkali activators

Blending Plastics Waste with Highly Available Jordanian Kaolin for Preparation of Alkali-Activated Mortars

Due to their lower energy demand, alkali-activated materials or geopolymers (GPs) are strong candidates to replace ordinary Portland cement binders in some applications. The present article attempts to investigate the possibility of incorporating plastics waste in place of silica sand filler in the GP mortars. The compressive strength, density, FTIR, XRD, BET and SEM of the prepared mortars were evaluated. Satisfactory compressive strength was achieved for metakaolin (MK)-based GP mortars containing plastic fillers (polyvinylchloride (PV), polystyrene (PS), polypropylene (PP) and polyethylene (PE)) which was dependent on the nature of plastic incorporated in the GP matrix: MKPV (30.3 MPa) > MKPS (15.8 MPa)~MKPP (15.9 MPa) > MKPE (9.1 MPa). The 28-day compressive strength of GP containing polyvinyl chloride was almost equivalent to that containing silica sand. Much lower values were obtained for the corresponding kaolin-based GPs (2.5, 2.8, 1.8 and 2.2 MPa, respectively). As reflected by FTIR absorption bands at 1447 and 1400 cm−1, the addition of plastic filler reduces absorption of CO2 from the atmosphere which enhanced dissolution of Al species from metakaolin. The morphology of GPs containing plastic fillers exhibited amorphous tissue-like structure compared to crystalline structure in the case of GP containing silica sand. However, both types of GPs exhibited lower porosity than previously prepared metakaolin-based GPs. Remarkably, poor adhesion of plastic filler to the GP binder was observed due to the inertness of plastic fillers toward alkali activators

Simultaneous Determination of B1, B2, B3, B6, B9, and B12 Vitamins in Premix and Fortified Flour Using HPLC/DAD: Effect of Detection Wavelength

Simultaneous determination of water-soluble B vitamins is a troublesome analytical procedure since they have greatly variable structures and acid-base properties which imposed difficulties on eluting them in short time and selecting wavelength of detection. The aim of the present study was to develop a simple method that overcomes these difficulties. The method was successful in simultaneous determination of B1, B2, B3, B6, B9, and B12 in premix and fortified flour by extracting vitamins with 0.1% (w/v) of ascorbate and ethylene diamine tetra-acetic acid (EDTA) solution followed by eluting using gradient mobile phase consisting of 0.03% trifluoroacetic acid aqueous solution (pH 2.6) and acetonitrile on high performance liquid chromatography (HPLC) instrument coupled with diode array detector (DAD). Elution of vitamins was completed within 9.3 min, and the lowest values obtained for limit of quantification (LOQ) for B1, B2, B3, B6, B9, and B12 were 0.6, 0.2, 0.8, 0.3, 0.5, and 0.7 μg/mL, respectively, at four wavelengths of 361, 280, 265, and 210 nm. In general, variation of wavelength of detection in the range from 210 to 361 nm affects sensitivity but had a marginal effect on the linearity and LOQ of the developed method and its application for determining B vitamins in premix and fortified flour. The 210 nm wavelength exhibited the highest sensitivity though resulted in higher values of B vitamins in fortified flour with respect to 265, 280, and 361 nm. Noteworthy, determination of B2 and B12 in the premix at 361 nm had relatively high RSD values compared to the lower wavelengths. Thus, wavelengths in the range from 265 to 280 may be more favorable over 210 and 361 nm. The method reported in the present work does not require any sample cleanup/preconcentration steps, and chromatographic elution was achieved in 9.3 min without the need for ion-pairing reagents

Transition Metal Complexes of Schiff Base Ligands Prepared from Reaction of Aminobenzothiazole with Benzaldehydes

Schiff bases have played significant roles in the development of inorganic or coordination chemistry. Three Schiff base (NB, CB and HB) ligands, prepared for the reaction of 2-amino-6-methoxy-benzothiazole with 2-Nitrobenzaldehyde, 2-chlorobenzaldehyde and 2,4-Dihydroxybenzaldehyed, respectively, were investigated for their transition metal complexes, which were prepared by reacting the ligand (2:1 molar ratio) with Co(II), Ni(II), Cu(II), Cd(II), Cr(III) and Fe(III) chlorides. The nature of the interaction between the metal ions and ligands (L) was studied with the aid of magnetic susceptibility, elemental analysis, FTIR and 1H-NMR spectroscopy. Based on the magnetic superstability and elemental analysis results, octahedral structures of the complexes, such as [ML2Cl2] or [ML2Cl(OH)], were proposed for Cu(II), Cd(II), Co(II) and Ni(II) in which the ligand (L:NB, CB or HB) is bidentate through the azomethine and benzothiazole nitrogen. For Cr(III) and Fe(III) complexes, octahedral ML2Cl(OH)2 or ML2(OH)3 structures were proposed, where one ligand is monodentate and the other is bidentate. The azomethine ν(-HC=N-) and 1H-NMR peaks of NB and CB were shifted to a higher frequency and downfield, respectively, upon complexation with metal ions. The bonding of OH groups of HB to Co(II), Cu(II) and Ni(II) enables π-backdonation from these metals to the azomethine of Schiff bases and the consequent shift of ν(-HC=N-) to a lower frequency and changes in the intensity of the 1H-NMR peak of OH. On the other hand, this backdonation was not evidenced in the FTIR of HB complexes with high-charge Cr(III) and Fe(III) ions