Surface modification of pine bark with quaternary ammonium groups and its use for vanadium removal

Ruichi Zhang,Tiina Leiviskä

doi:10.1016/j.cej.2019.123967

Ruichi Zhang, Tiina Leiviskä

Open Access

https://doi.org/10.1016/j.cej.2019.123967

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Abstract

Chemically modified pine bark was synthesized by using glycidyl trimethyl ammonium chloride (GTMAC) in the presence of sodium hydroxide. Optimization of the modification parameters was performed in order to maximize vanadium removal. Parameters included the initial NaOH concentration (0.01–2% w/v), GTMAC dosage (0.0067–0.0805 mol/g), modification time (1–6 h), modification temperature (40–80 ℃) and volume (25–100 mL). The optimal modification conditions were found to be 0.1% NaOH (w/v), 0.0134 mol/g GTMAC, 3 h and 60 ℃. The initial NaOH concentration played the most important role in successful modification while the GTMAC/NaOH ratio and volume had no significant effect under the studied conditions. Leaching of organic substances from the modified product was minor in comparison with raw pine bark. XPS analysis confirmed that quaternary nitrogen was successfully grafted onto the pine bark and that the BET surface area increased in the modification. The maximum vanadium adsorption capacity of the optimized product was found to be 32.3–35.0 mg/g at different temperatures (20 ℃, 15 ℃ and 5 ℃) at pH 4 with a contact time of 24 h, and the adsorption data was in very good agreement with the Freundlich and Redlich-Peterson models. The adsorption kinetics can be described well by the Elovich equation. Fitting the kinetic data with intra-particle diffusion and Boyd models showed that the adsorption process was controlled by both film and intra-particle diffusion, while intra-particle diffusion was the rate-limiting step. Regeneration studies demonstrated that, as a recyclable product, modified pine bark can be used effectively in real industrial processes for vanadium removal.

Highlights

Vanadium occurs widely in natural resources such as crude petroleum, uranium ores, phosphate deposits and magnetites but concentrated vanadium deposits are quite rare [1]
When the initial NaOH concentration was increased from 0.01% to 0.1% (w/v) (GTMAC dosage was kept constant at 0.0134 mol/g), vanadium removal efficiency increased significantly from 56% to 91% (Fig. 1a)
Quaternary ammonium-modified pine bark can be effectively used for vanadium removal

Summary

Introduction

Vanadium occurs widely in natural resources such as crude petroleum, uranium ores, phosphate deposits and magnetites but concentrated vanadium deposits are quite rare [1]. Due to the extensive use of vanadium and its suspected toxicity, the removal of vanadium from wastewaters has become an important issue in terms of environmental protection. Vanadium exists in different oxidation states in aqueous solution, with vanadium (V5+) as the major stable species in oxidation states [2]. The speciation of vanadium is highly influenced by the solution pH and vanadium concentration. Owing to the obvious advantages of adsorption such as simplicity and low cost, it is commonly used and reported for vanadium removal from aqueous solution [4,5,6]

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