Study of the Chromium(vi) Removal From Aqueous Systems by Cobalt Nanoparticles

Abstract

The cobalt nanoparticles (NPs-Co) were synthesized and applied in the removal of Cr(VI). The obtained nanomaterials presented magnetic properties and were characterized by the techniques of Transmission Electron Microscopy and X-ray diffraction. The NPs-Co, with a diameter of less than 50 nm, had a composition based on metallic cobalt and cobalt oxide. The NPs-Co were applied in the removal of Cr(VI) being evaluated different parameters such as time of equilibrium, initial pH, dose of NPs-Co, concentration of Cr(VI), and system temperature. The removal of Cr(VI) was favored at lower pH values, being about 100% at pH 2.0. With the increase of Cr(VI) concentration from 40.0 to 300.0 mg L-1 the removal decreased from 80 to 15%. The NPs-Co dose promoted an increase in removal reaching 90% at a dose of 1.0 g L-1. The removal process was spontaneous and endothermic, and the Langmuir isotherm model fit better to experimental data. The maximum removal capacity was approximately 70.0 mg g-1. The removal kinetics followed the pseudo-second order model. The mechanism of Cr(VI) removal occurred through adsorption by electrostatic interactions between CrO 4 2anion and Co-NPs, followed by reduction of Cr(VI) to Cr(III) and, lastly, co-precipitation of Cr(III) as Cr(OH) 3 on the NPs-Co.

Efficient Removal of Cr(VI) Ions by a Novel Magnetic 4-Vinyl Pyridine Grafted Ni3Si2O5(OH)4 Multiwalled Nanotube

“…The spent adsorbents are expected to be regenerated by ion exchange with OH – in the base solution, which is similar to the regeneration of cobalt nanoparticles. 67 The regeneration efficiency and reusability of Ni 3 Si 2 O 5 (OH) 4 - g -P4VP NTs was investigated in a batch process using 0.1 mol·L –1 KOH solution as the regenerant. There is no significant decrease in Cr(VI) adsorption capacity of Ni 3 Si 2 O 5 (OH) 4 - g -P4VP NTs after eight adsorption and desorption cycles ( Figure 14 ).…”

“…The magnetic Ni 3 Si 2 O 5 (OH) 4 - g -P4VP NTs possess abundant imine groups which exhibit electrostatic interaction with Cr­(VI). The spent adsorbents are expected to be regenerated by ion exchange with OH – in the base solution, which is similar to the regeneration of cobalt nanoparticles . The regeneration efficiency and reusability of Ni 3 Si 2 O 5 (OH) 4 - g -P4VP NTs was investigated in a batch process using 0.1 mol·L –1 KOH solution as the regenerant.…”

“…The spent adsorbents are expected to be regenerated by ion exchange with OH − in the base solution, which is similar to the regeneration of cobalt nanoparticles. 67 The regeneration efficiency and reusability of Ni The mechanism of heavy metal adsorption onto adsorbent particle consists of the following basic steps: liquid film diffusion, intraparticle diffusion, and mass action. 82 The rate-limiting step is usually film diffusion or/and intraparticle diffusion since the mass action is very rapid and negligible.…”