Adsorptive Behavior of Arsenic(III) Ions from Aqueous Solution onto Forestry and Agricultural Waste Biochar Pyrolyzed at 400°C

S.K Gunatilake

doi:10.4038/suslj.v14i2.7699

Abstract

Sorption capacity of two different biochar (saw dust and rice straw) was evaluated in the recovery of arsenic from aqueous solutions. Biochar from rice straw and saw dust were obtained from pyrolysis of biomass at 400°C. The optimum sorption conditions were studied for different concentrated monometallic system. Sorption studies were performed at different pH, contracting time and different initial metal ion concentration in the batch mode. The optimum pH was 3 for recovery of As(III) and kinetic studies yielded an optimum equilibrium time of 50-60 minutes with an adsorbent dose of 1 g/L and initial concentration ∼20 mg/L for As(III) ions. As(III) ions in aqueous solution were transported to biochar surface through adsorption and intra-particle diffusion process. Experimental data for As(III) ions was fitted a Langmuir model with R2 value for As(III) 0.969, 0.879 for saw dust and rice straw respectively. The Freundlich constant, KF values for removal of As(III) ions by saw dust and rice straw were 0.9127, 0.8951 respectively. The 1/n value for arsenic ions obtained from saw dust and rice straw were 0.209, 028 and indicate the normal sorption of As(III). The values indicated the affinity of the sorbent towards the uptake of As(III) ions were favorable and rice straw and saw dust biomass can be used to remove Arsenic(III) ions from aqueous phase.

Highlights

Recent years, biosorption methods were extensively used for removal of heavy metals from aqueous phase since such methods have been proven to be an efficient technique for the sequestration of pollutants in wastewater
It was observed that adsorption capacity about 6.8 mg/g of As(III) ion from saw dust biochar was attained in first 35 minutes and concentration became almost constant after 40 minutes (Figure 1)
Adsorption of arsenic onto rice straw biochar was optimum around 50 minutes duration and adsorption capacity was 5.7mg/g

Summary

Introduction

Biosorption methods were extensively used for removal of heavy metals from aqueous phase since such methods have been proven to be an efficient technique for the sequestration of pollutants in wastewater. Such methods are usually low cost as the absorption materials are mostly by-product of agricultural and other industrial wastes. That pyrolyzed from biomass under no or very low oxygen condition are mostly stable and having a superior ability to retain heavy metals Such materials are beneficial in decreasing the bioavailability of pollutants and mitigate their ecological toxicities. Biochars made from agricultural wastes, including fruit peels , pine needles , grass , hardwood , crop straw and woodchip have been widely investigated for removing toxic heavy metals from aqueous solution replacing costly chemisorption methods

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