Potential of waste pumice and surface modified pumice for hexavalent chromium removal: Characterization, equilibrium, thermodynamic and kinetic study

International audienceThe sorption potential of natural (NP) and surface modified pumice using MgCl2 (MGMP) as an abundant and low cost geo-material for the removal of Cr(VI) ion was investigated. The influence of contact time, solution pH, initial metal concentration, amount of absorbents and solution temperature was studied. Natural and modified adsorbents were characterized by means of XRD, XRF, SEM and FTIR technologies. Maximum sorption was observed at pH 1 and 100 mg/L metal concentration. Equilibrium data were accurately fitted onto Langmuir, Freundlich and Temkin isotherms, showing the heterogeneous nature of the adsorbents; maximum sorption capacity according to the Langmuir isotherm were 87.72 mg/g and 105.43 mg/g for NP and MGMP, respectively, showing a high sorption potential if compared to adsorbents used for Cr(VI) removal. Intra-particle model demonstrated that film diffusion was the rate-limiting step instead of intra-particle diffusion, as confirmed from the analysis of pseudo-second order rate constants, showing an absence of limitation due to pore diffusion. Relevance of pumice was confirmed since high regeneration yields were obtained, 94.3% in acidic conditions (1 M HCl) for spent non-modified pumice and 91.3% in alkaline conditions (4 M NaOH) for spent modified pumice

Comparing the performance of granular coral limestone and Leca in adsorbing Acid Cyanine 5R from aqueous solution

The effect of granular coral limestone and Leca as adsorbents for removing Acid Cyanine 5R (AC5R) from aqueous solution was studied. The optimum pH and adsorbent particles size in both adsorbents were determined to be 3 and 297 μm, respectively. The optimum dosages of coral limestone and granular Leca were 0.150 and 0.145 g/mg of dye, respectively. Also, results have shown that the adsorption efficiency by both coral limestone and Leca increased with the decreasing adsorbent particles size. Moreover, under similar conditions, the maximum removal efficiency by granular coral limestone and Leca was 94% and 88%, respectively. The results revealed that the performance of granular coral limestone was better in AC5R removal than that of Leca granulated under such condition. In total, granular coral limestone and Leca act as suitable adsorbents for removing dye pollutants from an aqueous solution