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Three carbonaceous porous materials (biochar and activated carbon) were developed from the Tectona grandis tree sawdust. The applied process of two-stage preparation included pre-treatment through hydrothermal carbonization at 190 °C and subsequent pyrolysis at 800 °C. Two chemical activating agents (K2CO3 and ZnCl2) were used to prepared activated carbons (K2CO3-AC and ZnCl2-AC), respectively. They were characterized by textural property, morphology, and surface element components and applied to remove Cr(VI) from solution at various solution pH values and initial Cr(VI) concentrations. Results showed that the textural parameters (SBET and VTotal) of the prepared material were 1757 m2/g and 1.027 cm3/g for Zn-Cl2-AC, 1013 m2/g and 0.418 cm3/g for K2CO3-AC, and 792 m2/g and 0.345 cm3/g for biochar. The adsorption process reached the highest efficiency at pH 3.0. The Langmuir maximum adsorption capacity indicated the decreasing order: ZnCl2-AC (127 mg/g) > K2CO3-AC (103 mg/g) > biochar (83.5 mg/g). The removal mechanism of Cr(V) from solution was regarded as an adsorption-coupled reduction, namely (1) partial reduction of Cr(VI) into Cr(III) during the adsorption process and (2) adsorption of the Cr(VI) anions through electrostatic attraction and pore filling and the reduced Cr(III) cations through complexation, Cπ–cation interaction, cation exchange, and pore filing. Therefore, the prepared biochar and activated carbon can server as promising adsorbents to efficiently remove both Cr(VI) and Cr(III) from water.

This study focuses on the investigation of the performance of Litchi chinensis sonn peels in a simulated fixed bed column in sequestering Cr(VI) by breakthrough curve analysis using Aspen Adsorption® V8.4. The breakthrough curve analysis was conducted by: 1) varying initial concentration at a constant flow rate and constant bed height, 2) varying flow rate at a constant initial concentration and constant bed height, and 3) varying bed height at constant flow rate and constant initial concentration. The good adsorption capacity was implied by a longer breakthrough time so as to make use of the peels of Litchi chinensis sonn for a longer period of time before there was a need to replace or to regenerate. Increasing the volumetric flow rate at constant initial sorbate concentration and bed height increased the breakthrough time. Increasing the initial sorbate concentration at constant volumetric flow rate and bed height decreased the breakthrough time. Increasing the bed height at a constant volumetric flow rate and initial sorbate concentration increased the breakthrough time. Longer breakthrough time denotes a better adsorption capacity. The longest breakthrough time was 335 s with volumetric flowrate at 1x10-3 L s-1 , initial sorbate concentration at 20 mg L-1 , and a bed height of 0.7 m. The shortest was 6.63 s with a volumetric flow rate at 1x10-2 L s-1 , initial sorbate concentration at 200 mg L-1 , and a bed height of 0.2m.

Biosorption is becoming an attractive alternative for the removal of heavy metal from contaminated wastewaters since it offers low capital and operating costs. It has a great potential on heavy metal decontamination and the possibility of metal recovery. The study evaluated the performance of water hyacinth (Eichhornia crassipes) in a fixed bed column on sequestering heavy metals present in wastewaters. Column breakthrough curves at varying parameters were evaluated. The study used Aspen Adsorption® to simulate the biosorption process. Analysis of breakthrough curves for the single metal system shows that increasing both influent flow rate and initial metal concentration reduces the metal uptake of the column, while increasing bed height enhances the metal uptake of the column. Presence of both Cd(II) and Cu(II) in the system promotes competitive sorption processes. Analysis of the breakthrough curves for the binary metal system showed that copper ions adsorbed to the adsorbent are replaced by cadmium ions when the maximum capacity of the column is reached. This leads to the outlet concentration of Cu(II) exceeding its initial concentration. This phenomenon shows that Cd(II) has more affinity with E. crassipes than Cu(II).

This study investigated the potential of powdered pineapple crown leaves (PCL) as an effective adsorbent for the removal of crystal violet (CV) from aqueous solution using batch and column studies. The PCL was simply washed, dried, and powdered prior to adsorption. FTIR analysis of PCL surface before and after adsorption revealed that hydroxyl and carboxyl functional groups are among the groups responsible for surface bonding with CV. SEM photographs of the adsorbent before and after revealed clumping on the surface of PCL, possibly indicating the sites where CV had been adsorbed. Elemental analyses through XRF revealed that K+ ion is a major part of PCL, and this could explain the affinity of CV for PCL through cation-π interactions. Batch adsorption studies were carried out as a function of biosorbent dose and initial dye concentration. The %removal of PC increased as biosorbent dose was increased, but the biosorbent capacity decreased. This was attributed to scattering of CV to more active sites in PCL. Biosorbent capacity increased as the initial dye concentration was increased, while %removal decreased. This was due to the faster saturation of the substrate. For equilibrium studies, Langmuir and Freundlich isotherm models were applied. The equilibrium data fitted well to Langmuir isotherm with a maximum monolayer adsorption capacity of 6.4935 mg/g. The relatively high maximum biosorption capacity coupled with the absence of chemical treatment needed before adsorption makes PCL an effective and sustainable biosorbent for the removal of CV.