Bengal gram husk (channa dal), seed coat of Cicer arientinum was collected from a legume seed-splitting mill. The Bengal gram husk (bgh) was washed extensively in running tap water to remove dirt and other particulate matter. Following this, washing and boiling in distilled water was done repeatedly to remove color. The washed and boiled Bengal gram husk was oven dried at 105°C for 24 h stored in a desiccator and used for biosorption studies in the original piece size.

An aqueous stock solution (1000 mg/L) of Fe(III) ions was prepared using ferrous ammonium salt as follows: 7.022 g of crystallized ferrous ammonium sulphate was dissolved in 500 mL of water and 50 mL of 1: 1 sulphuric acid was added. The solution was warmed and oxidized with approximately 0.1 % potassium permanganate solution until the solution remained faintly pink made upto 1 L with distilled water²². The pH of the solution was adjusted using 0.1 N HCl or NaOH. Fresh dilutions were used for each study.

The biosorption capacity of bgh was determined by contacting various concentrations (l0-100 mgL^-1) of 100 mL iron solution in 250 mL conical flasks, with 1 g of bgh. The mixture was shaken in a rotary shaker at 120 rpm followed by filtration using Whatman filter paper (No. 1).

The filtrate containing the residual concentration of Fe(III) was determined spectrophotometrically at 530 nm after complexation with sodium salicylate²². For the determination of rate of metal biosorption by bgh from 100 mL (at 10, 20, 50, 100 mgL^-1), the supernatant was analysed for residual Fe(III) after the contact period of 15, 30, 60, 120, 180, 240 and 300 min. The effect of pH on Fe (III) sorption by bgh, was determined at pH values of 2, 2.5, 3, 3.5 and 4. The effect of adsorbent dosage was studied at different dosages ranging from 1 to 40 g/L with varied metal concentrations of 10, 20, 50 and 100 mg/L.

Adsorption isotherm studies were carried out with ten different initial concentrations ranging from 20 to 500 mg/L of Fe(III) while maintaining the adsorbent dosage at 1 g/100 mL. Langmuir and Freundlich models were applied to the adsorption isotherm and different constants were generated. The Langmuir and Freundlich adsorption parameters and correlation coefficient were also calculated from the adsorption isotherm data.

In order to determine the functional groups responsible for metal uptake, an un-reacted bgh sample and bgh pretreated with 100 mg/L iron solution were analysed using a Fourier transform infrared spectrometer.