Modifications of coconut pith as mercury adsorbents for industrial applications

Contamination of wastewater by mercury ions poses a great concern due to its toxicity and threat to the public health and ecological systems. This study was conducted to investigate utilization of coconut pith (CP) as adsorbents for the removal of mercury ions, Hg(II) and MeHg(II). The CP underwent several modification processes: pre-treatment; silane-grafting and dye-loading, aiming for better Hg(II) and MeHg(II) adsorption performance. The adsorption performance study was conducted in batch and continuous adsorption system. The physical and chemical properties of CP adsorbents changed after modifications. The silanegrafting using mercaptopropyltriethoxysilane (CP-MPTES) and dye-loading using Reactive Red 120 (CP-RR) resulted in the highest removal efficiency towards both mercury ions. This is due to the presence of functional groups which have high affinity towards both mercury ions. Batch adsorption studies found that the adsorption capacity of both mercury ions was dependent on initial pH, adsorbent dosage, initial concentration, contact time and temperature. The maximum adsorption capacity of Hg(II) onto CP-Pure, CP-MPTES and CP-RR was 2.60, 2.61, and 2.60 mmol/g, while 0.50, 1.13 and 0.76 mmol/g was observed for MeHg(II), respectively. The equilibrium and kinetic data analyses found that the mechanism of mercury ions adsorption onto CP adsorbents is a combination of physical and chemical processes. The high regenerability was only observed in Hg(II) adsorption. The competence of Hg(II) and MeHg(II) adsorption in oilfield produced water and natural gas condensate samples, respectively, found that the presence of other metal ions reduced the adsorption performance of the mercury ions. The mercury ion adsorption in continuous fixed-bed adsorber studied at various conditions showed that the increase of flow rate and initial concentration caused the exhaustion time (texh) to occur earlier, but higher bed height prolonged the texh. The breakthrough curves of mercury ions adsorption were analyzed using Thomas, Bohart-Adam, Yoon-Nelson, Wolborska and Clark models. Thomas and Yoon-Nelson models fit most of the experimental data. However, empty bed contact time analysis found that the Yoon-Nelson model is more applicable to predict the breakthrough curves of the scale-up adsorber. The regenerability studies had low performance towards Hg(II) adsorption and fair performance towards MeHg(II) adsorption. In overall, the batch and continuous mercury ion adsorption results show the potential application of the CP adsorbents as low-cost adsorbent for industrial mercury ion removal process

Silver ion adsorption using alkali and organosilane modified coconut pith biosorbents

The coconut pith biosorbents were prepared by modifying coconut pith (CP) with sodium hydroxide and bis(triethoxysilylpropyl) tetrasulfide to enhance its sorption capacity and selectivity toward silver ion [Ag(I)]. It was found that the Ag(I) sorption capacity of pure CP, CP modified with sodium hydroxide, and CP modified with bis(triethoxysilylpropyl) tetrasulfide was 0.50, 0.48, and 0.62 mmol/g, respectively. The Ag(I) equilibrium data were best fitted to the Langmuir isotherm model, whereas the kinetic data obeyed the pseudo-second-order kinetic model with the anticipation of the film diffusion as the rate-limiting step. The sorption process was generally governed by a combination of physical and chemical sorption mechanisms. The Ag(I) sorption capacity and selectivity of coconut pith biosorbents were low as compared with other metal ions

Adsorptive removal of benzene from aqueous solution by surfactant modified banana trunk as adsorbents

The adsorptive removal of benzene from aqueous solution by four types of surfactant modified banana trunk (BT) adsorbents was investigated through batch adsorption experiments. The surface morphology and functional groups determination were conducted BT adsorbents indicating the significant changes were observed after modifications. The adsorption results indicated that the non-ionic surfactant (i.e. Triton-X 100) modified BT has the highest adsorption capacity (57.52 µmol/g) and its adsorption capacity significantly affected by the increase of temperatures, benzene concentrations and contact time

Silver adsorption enhancement from aqueous and photographic waste solutions by mercerized coconut fiber

The mercerized coconut fiber (CF-NaOH) was prepared by treating the pristine coconut fiber (CF-Pure) with NaOH solution. The morphology and chemical composition of CF-Pure changed after mercerization process. The maximum Ag(I) adsorption capacity of the CF-Pure and CF-NaOH was 0.502 and 0.612 mmol/g, in which the equilibrium data fitted to the Freundlich and Langmuir isotherm models, respectively. The Ag(I) adsorption rate also increased by using CF-NaOH and the kinetic data of both CF-Pure and CF-NaOH obeyed the pseudo-second order kinetic model. The enhancement of Ag(I) adsorption selectivity from photographic waste solution was also observed for the CF-NaOH

Removal of Elemental Mercury by Coconut Pith Char Adsorbents

AbstractCoconut pith (CP), which is abundantly available and cheap, has the potential of being used as low-cost adsorbents for elemental mercury removal. In this study, the preparation of chars was carried out through the carbonization of CP at three different environment conditions: (a) open reactor under nitrogen flow; (b) closed reactor under nitrogen environment; and (c) closed reactor under ambient environment; at the temperature of 700°C. The results show that the chemical, physical, morphological and spectral properties of the adsorbents greatly influenced by the environment of carbonization used. The highest Hgo adsorption capacity was observed for CCA700 (2395.98 μg/g), followed by CCN700 (2052.49 μg/g), and CFN700 (1416.92 μg/g). These results demonstrated that coconut pith derived chars could be potential as low-cost adsorbent alternatives for the removal of elemental mercury in gas streams

Characterization of natural zeolite for adsorptive removal of antibiotics from aqueous solution

The persistent existence of antibiotics in sewage wastewater treatment plants in recent years has emerged as a serious concern. In this study, natural zeolite (NZ02) obtained from China was employed as an adsorbent to remove tetracycline (TC) from aqueous solution. The characterization results show that the NZ02 consists of quartz, clinoptilolite-Na and heulandite having the CEC of 62.18cmol/kg and the surface area of 36.646m2/g. Adsorption results show that the maximum adsorption capacity of TC on NZ02 was 19.30mg/g and the equilibrium data followed theLangmuir adsorption isotherm model

Synthesis and characterization of secondary amine-functionalized silica for CO2 capture

As one of commonly used technique for carbon dioxide (CO2) removal, amine-absorption also required high amounts of energy for adsorbent regeneration and problems of equipment corrosion during chemical holding may happened. Alternatively, amine-impregnated solid adsorbent received wide attention for CO2 removal. However, there are limitations on the adsorbents’ adsorption capacity and their hydrolytic stability. In this study, amine-functionalized silica (T-Si) adsorbent was synthesized via oil-in-water emulsion technique using centrimonium bromide (CTAB) as surfactant, ethanol as oil phase, and tetraethyl orthosilicate (TEOS) as silica precursor followed with impregnation with secondary amine (tetraethyl pentamine, TEPA). Results indicated that T-Si2 adsorbent has a surface area of 10.7338 m2/g, presence of amine group (N-H) peaks in the FTIR spectra, and is thermally stable up to temperature of 170 oC. CO2 adsorption study also shows that the T-Si also performed higher adsorption capacity (0.63 mmol/g) towards CO2 compared to the blank Si adsorbent (0.33 mmol/g). The obtained experimental data show a good fitting into Sips adsorption isotherm which indicate a multilayer adsorption that happen on a heterogenous surface. The findings of this study show that the introduction of amine groups from TEPA offers improvement towards CO2 capture due to the reaction with amine groups

Natural zeolite characterization for adsorptive coagulation flocculation (ACF) removal of ammonium in drinking water treatment process

The naturally occurring zeolite (N Z01) was characterized and used as an adsorbent for the removal of ammonium (N-NH4+) from water. The characterization results show that the NZ01 is mainly composed of clinoptilolite, quartz and plagioclase and has the cation-exchange capacity (CEC) of 64 cmol/kg. Batch adsorption results show that the best ammonia removal was at pH close to that of the natural water (= pH 7). The increase in initial ammonium nitrogen concentration from 5 to 50 ppm resulted in an increase of the adsorption capacity from 0.64 to 15.1 mg NH4+-N/g. The Jar test experiments indicate the introduction of the NZ01 enhanced the ammonium removal efficiency. All these results demonstrate that the NZ01 is potential to be used for the removal of ammonium in drinking water treatm ent process

Removal of elemental mercury from gas stream using sulfur-functionalized silica microspheres (S-SMs)

Silica microspheres (SMs) was synthesized and modified through impregnation with elemental sulfur (S8) and carbon disulfide (CS2) to produce sulfur-functionalized silica microspheres (S-SMs). The morphology of SMs did not change after modification, however, its pore characteristics and sulfur content as expected did change significantly. The elemental mercury adsorption rate and capacity from synthetic gas stream increased with the presence of sulfur compounds in the SMs. For instance, at bed temperature of 50 °C, the adsorption capacity and rate of adsorbents (SMs, S8-SMs and CS2-SMs) were (5.71, 37.24, and 83.41 µg/g) and (0.319, 0.749, and 1.922 µg Hg°/g min), respectively. It was observed that the adsorption rate and the capacity increased with bed temperature only for the SMs, while decreasing for the S-SMs. This might be due to different governing adsorption mechanisms for both types of adsorbents