Abstract
The previously-obtained and characterized hybrid pectin-based beads containing agar-agar and guar gum, as well as sole pectin beads (P, for comparison) were examined for zinc ions sorption and desorption properties. The sorption kinetics and equilibrium in the studied system was described by two kinetic models (pseudo-first- and pseudo-second-order) and two isotherms (Langmuir and Freundlich), respectively. The desorption kinetics and equilibrium was also investigated by applying various inorganic acids (nitric, hydrochloric, and sulfuric acid) of various concentrations. In the case of guar gum additive, no significant change in sorption capacity compared to sole pectin beads was observed (q: 37.0 ± 2.6 and 34.7 ± 2.0 mg/g, respectively). Addition of agar-agar significantly decreased the sorption capacity to 22.3 ± 1.0 mg/g, but stripping of zinc(II) ions from this biosorbent was complete even with very diluted acids (0.01 M). Total desorption of zinc from sole pectin and pectin-guar gum beads required acid solution of higher concentration (0.1 M). Sorption rates for all biosorbents are roughly the same and maximum sorption is achieved after 4–5 h. Obtained results and the advantage of our sorbent’s shape formation ability, make the pectin-based biosorbents interesting alternative for zinc(II) ions removal.
Highlights
Heavy metals, present in the waste waters originating from various branches of industry and agriculture, are a serious environmental hazard
At high dose of the sorbent, the majority of metal ions were adsorbed, but some active sites remained unsaturated, which resulted in decrease of the sorption capacity of metal ions per unit mass of adsorbent and increase of percentage of zinc removal
The highest zinc removal was achieved at the sorbent dose ≥ 3 g/L
Summary
Present in the waste waters originating from various branches of industry and agriculture, are a serious environmental hazard. Heavy metals contaminate ground waters, air, soil and may be accumulated in humans, animals and plants. Due to the enormous zinc usage in many branches of the industry, it is introduced into the environment. The concentrations of zinc in wastewaters depend on the origin and may be, for example, 500 mg/L (from electroplating industry) [2], 75 mg/L (from the electroplating industry in Greece) [3], 61.88 mg/L (from production of viscose rayon) [4], 12 mg/L (from a plating plant) [5], 10 mg/L (from a closed mine of zinc and lead) [6], and 6.6 mg/L (rinsing water of degreasing and metal plating) [7]. Since the limits of zinc in wastewater introduced into environment range from
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