INVESTIGATION OF MODIFIED CEDAR NUT SHELL-BASED SORBENTS

Abstract

The investigation was carried out to establish influences of thermal, chemical and thermochemical modifications on compositions of functional groups of the sorbents based on nut shells of the Siberian cedar (Pinus sibirica) and their physical and chemical properties. Samples of natural cedar nut shells (CNS) were thermally-modified at T=300 °С and analyzed by the methods of potentiometric titration and Fourier-transform infrared spectroscopy. It has been established that thermally-modified CNS possess 1.5–1.7 and 2.3–4.3 times as many hydroxyl and carboxyl groups in the constitution of sorbents grading 0.1–0.5 and 0.55–0.75 mm, respectively, as natural CNS. Chemical modification was carried out in nitric acid solutions with various concentrations (0.5–5n). It has been shown that being treated with 5n HNO3, the samples grading 0.55–0.75 mm possess 3.5 times as many carboxyl groups as natural CNS, while the samples grading 0.1–0.5 possess an increased number of hydroxyl groups only. Thermochemical modification was carried out in 2 stages: first, firing at a temperature of 300 °С, then chemical modification in HNO3 solutions with various concentrations. It has been revealed that this modification results to increasing predominantly hydroxyl groups in the constitution of carbon sorbents. The isotherm of sorption of copper (II) ions by the samples of modified CNS describes microporous solids with a relatively small outer surface, whereas the sorption isotherm of zinc (II) ions describes polymolecular adsorption onto both porous and macroporous adsorbents. The investigation has revealed that the sorbents being chemically and thermochemically modified with 5n nitric acid are most effective to extract copper ions.