Development of a Disposable Pipette Extraction Method Using Coffee Silverskin as an Adsorbent for Chromium Determination in Wastewater Samples by Solid Phase Extraction

A procedure using disposable pipette tips adapted for solid-phase extraction, known as DPX‑SPE, was used as an alternative way for the chromium determination in wastewater samples. DPX-SPE consists of a device which allows a dynamic contact between the sample and the solidphase. A residue obtained from the processing of coffee beans, denominate coffee silverskin, was used as a new adsorbent. Characterization techniques revealed properties of lignocellulosic materials with potential application for chromium adsorption. The parameters including adsorbent mass (25.00 mg), elution solvent (0.1 mol L−1 HCl, 200 μL) and pH (2.0) were optimized. Thus, 1.00 mL of deionized water for conditioning, 4.00 mL of sample, 2 extraction cycles and 1 elution cycle were the employed conditions. Enrichment factor of 12, limit of detection of 6.00 μg L−1 and relative standard deviation (RSD) 1.3% (n = 3) were obtained. The method proved to be fast, cheap, environmentally friendly, and simple, providing good recoveries (104-113%), and it was satisfactorily applied in real samples.

Effect of Lattice Substitution on Adsorption of Hexavalent Chromium by Montmorillonite, Nontronite, and Beidellite

This work aims to evaluate the effect of lattice substitution on adsorption of hexavalent chromium by three kinds of typical clay minerals, and its common isomorph via experiments and calculations were performed based on density functional theory. The experiments (25 °C, 4 h, pH = 4 and without stirring) confirmed an order of adsorption capacity as follows: Montmorillonite (12 mg/g) > Nontronite (9 mg/g) > Beidellite (8 mg/g). Accordingly, the Mulliken populations, density of states, and band structures of the mineral models with the structural Al, Mg, Fe(II), Fe(III), and Al (in tetrahedrons) on behalf of five species of isomorph were calculated. The calculation results explain the differences between hexavalent chromium adsorption capacity of five kinds of isomorph by means of atom, key populations, overlapping valence electron orbitals, and the variation of energy band. However, no overlapping orbitals were observed in the adsorption system with structural Mg. It is implied that the structural Mg has little influence of hexavalent chromium adsorption. In conclusion, our study contributes to achieving a better understanding of modified clay minerals materials applications.

A Comparative Study on Hexavalent Chromium Adsorption onto Chitosan and Chitosan-Based Composites

Chitosan (Cs)-based composites were developed by incorporating silica (Cs–Si), and both silica and hydroxyapatite (Cs–Si–Hap), comparatively tested to sequester hexavalent (Cr(VI)) ions from water. XRD and FT-IR data affirmed the formation of Cs–Si and Cs–Si–Hap composite. Morphological images exhibits homogeneous Cs–Si surface, decorated with SiO2 nanoparticles, while the Cs–Si–Hap surface was non-homogeneous with microstructures, having SiO2 and Hap nanoparticles. Thermal analysis data revealed excellent thermal stability of the developed composites. Significant influence of pH, adsorbent dose, contact time, temperature, and coexisting anions on Cr(VI) adsorption onto composites was observed. Maximum Cr(VI) uptakes on Cs and developed composites were observed at pH 3. The equilibration time for Cr(VI) adsorption on Cs–Si–Hap was 10 min, comparatively better than Cs and Cs–Si. The adsorption data was fitted to pseudo-second-order kinetic and Langmuir isotherm models with respective maximum monolayer adsorption capacities (qm) of 55.5, 64.4, and 212.8 mg/g for Cs, Cs–Si, and Cs–Si–Hap. Regeneration studies showed that composites could be used for three consecutive cycles without losing their adsorption potential.

Pengaruh Konsentrasi Aktivator Asam Fosfat (H3PO4) pada Pembuatan Karbon Aktif dari Sabut Kelapa terhadap Adsorpsi Logam Kromium

Chromium is one of the hazardous heavy metal contained in the industrial wastewater. It can be reduced by various methods, such as adsorption. The purpose of this study was initialized an activated carbon from coconut fiber by various phosphoric acid (H₃PO₄) activator concentration (0,1M; 0,5M; 1M; 1,5M; 2M) and variation of contact time (30; 60; 90; 120; 150; 180 minutes) to obtain optimum adsorption capacity of chromium. Analysis of the activated coconut fiber carbon by SAA obtained a surface area of 53,39 m²/g. The potassium chromate (K₂CrO₄) solution was adsorbed by the adsorbent and then analyzed by a UV-VIS Spectrophotometer to measure the chromium content. This study proved that chromium adsorption by activated coconut fiber carbon was increased by the time until reaching optimum condition. Enhancement of adsorption capacity was directly proportional as the more concentrated phosphoric acid activator. Maximum adsorption capacity obtained was 3,464 mg/g and the optimum condition was at contact time of 150 minutes with the phosphoric acid activator concentration of 2M.

Removal of Cr by Modified Biochar Derived from Corn Husk

In this study, the physicochemical properties of modified biochar using different methods, such as physical (CO2, steam) and chemical (KOH and H3PO4) methods, were estimated by X-ray diffraction, N2 adsorption-desorption, field-emission scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. The performance of chars was evaluated using a Cr adsorption performance test. Among various chars modified in this study, CHC-P modified by H3PO4 showed the highest chromium adsorption efficiency. The adsorption efficiency was affected by the high nano-porosity, large surface area, and surface oxygen-containing functional groups.