Removal of cadmium (II) from aqueous solutions by adsorption on agricultural waste biomass

Abstract

This paper reports the feasibility of using various agricultural residues viz. sugarcane bagasse (SCB), maize corncob (MCC) and Jatropha oil cake (JOC) for the removal of Cd(II) from aqueous solution under different experimental conditions. Effect of various process parameters, viz., initial metal ion concentration, pH, and adsorbent dose has been studied for the removal of cadmium. Batch experiments were carried out at various pH (2–7), adsorbent dose (250–2000 mg), Cd(II) concentration (5–500 mgl⁻¹) for a contact time of 60 min. The maximum cadmium removal capacity was shown by JOC (99.5%). The applicability of Langmuir and Freundlich isotherm suggests the formation of monolayer of Cd(II) ions onto the outer surface of the adsorbents. Maximum metal removal was observed at pH 6.0 with a contact time of 60 min at stirring speed of 250 rpm with an adsorbent dose of 20 g l⁻¹ of the test solution. The maximum adsorption of cadmium (II) metal ions was observed at pH 6 for all the adsorbents viz; 99.5%, 99% and 85% for JOC, MCC, and SCB, respectively. Order of Cd(II) removal by various biosorbents was JOC > MCC > SCB. JOC may be an alternative biosorbent for the removal of Cd(II) ions from the aqueous solution. FT-IR spectra of the adsorbents (before use and after exhaustion) were recorded to explore number and position of the functional groups available for the binding of Cd(II) ions on to studied adsorbents. These results can be helpful in designing a batch mode system for the removal of cadmium from dilute wastewaters.

Introduction

Contamination of wastewater with metal ions such as cadmium, chromium, arsenic, nickel and zinc is an ongoing problem due to their toxicity. These metals are toxic even at very minute concentrations [1]. Presence of metal ions is of special concern as they can accumulate in different components of the environment. It is well known that heavy metals can damage nerves, liver and bones and also interfere with the normal functioning of various metallo-enzymes [2], [3], [4], [5]. The adverse effects of cadmium on human beings include high blood pressure, kidney damage, destruction of testicular tissues and red blood cells. Cadmium ions can replace Zn(II) ions in some metallo-enzymes, thereby affecting the enzyme activity [6]. From electro-plating industries, batteries, phosphate fertilizers, mining, pigments, stabilizers and alloys, cadmium finds its way to the water streams through wastewaters [7], [8]. The permissible limits of cadmium for the discharge of wastewater is 0.1 mg l⁻¹ in India.

From wastewater, heavy metals are usually removed by precipitation technology using hydroxides, carbonates and sulphides [9], [10], [11]. Each method has its own benefits and limitations [12], [13]. A variety of microbial and other biomass types has been reported to have good biosorption potential and such materials have been suggested for use in wastewater treatment for metal removal [14], [15], [16], [17], [18]. Efficient and environment friendly adsorbents are still needed to reduce heavy metal content in wastewaters to acceptable level at affordable costs.

Abundant waste materials (or products) from industrial and agricultural activities may be potential inexpensive alternatives for heavy metal removal. In recent years, several agricultural wastes have been tested for their heavy metals removal efficiency from simulated wastewaters. Activated carbons prepared from some agricultural wastes [19], [20], [21], [22], [23], various industrial waste such as fly ash [24], waste rubber [25], animal bones [26], etc. are few examples of low-cost materials used in the removal of Cd(II) and other heavy metal ions from the wastewater.

Sugarcane bagasse (SCB), a byproduct of cane sugar processing, is generated in large quantities in India. Bagasse is either used as fuel by sugar mills or a raw material for paper manufacturing. Maize corncobs (MCC) are highly voluminous, costless agricultural waste of corn milling process. They have a bulk density of 0.320 g cm⁻³ for a particle size range of 0.85–2.00 mm. MCC are very rich in cellulose and hemi-celluloses which comprises ≈80% of the dry matter. They contain many polymeric materials that possess different functional groups. Jatropha crop has recently been introduced in Northern India for biodiesel recovery from its seeds. There is no reported use of the Jatropha oil cake (JOC) generated in the process of biodiesel recovery from its seeds. Recently JOC has been used as an effective adsorbent for the removal of heavy metal ions especially Cr(VI) from the aqueous solutions [27]. In the present work, removal of cadmium ions by JOC, MCC and SCB has been studied under different experimental conditions. The influence of different process parameters, such as initial metal ion concentration, pH and adsorbent dose has been investigated.