The directory of “Agency for Toxic Substances and Disease Registry Priority List of Hazardous Substances” offer top 10 positions for heavy metal ions due to its toxicity and potential exposure from a wide range of sources.
Indiscriminate disposal of toxic metal ions are still continuing and even increasing in developing countries. Coimbatore city is well known for small and medium scale electroplating industries. Nickel plating is most common process in the studied area and high concentrated effluent in huge volume is discharged per day, even at small units. Nickel is considered a moderately toxic element (< 0.5mg.L) comparing with other transition metals. Exposure to nickel is associated with respiratory cancer, dermatitis, gastrointestinal distress, chronic bronchitis, cardiovascular, kidney diseases and a skin disorder known as nickel-eczema.
Thence, efficient removal of Ni(II) ions from industrial wastewaters are the prime need of concern. Adsorption is among the most common methods employed for heavy metal ion trapping due to its simplicity, feasibility and effectiveness. Biosorbents ensures maximum sorption capacity and a best alternative for non-degradable activated carbons. Herein, chemically modified and nano sized biosorbents are prepared, characterized and equilibrium parameters are experimentally investigated. To the best of our knowledge, there has yet to be any report on Ni(II) ion removal using novel biosorbents.
Experimental SectionMaterials Goat Teeth (collected from local butcher shop, detached from jaw bone, washed well with running water to eliminate colloidal impurities then sun dried for prolong usage). Hydrochloric acid and Nickel nitrate salt of analytical grade was procured from Merck. Doubly distilled water was used to prepare stock and subsequent aliquot solutions. Preparation Nano-biosorbentTreated Goat Teeth(TGT)ref was weighed accurately about 40 grams for desizing to nanoscale level by top down approach using Planetary Ball Mill (Model- VBCC/PM/24-13/14) equipped with Tungsten Carbide bowl and 2 mm balls.
40 grams of the same was milled for 5 hours at 260 rpm revolutions and the agglomerated powder material was stored in an air tight container and named as NTGT. CharacterizationAtomic Force Microscopic (AFM) AnalysisAtomic Force Microscopic analysis offers visualization in three dimensions and surface roughness. Individual particles and groups of particles can be resolved finer, compared to other microscopic techniques. The top and 3 dimensional view (20µm X 20µm X 300 nm) of the nano particles are depicted in figures 1, 2 respectively. The thickness of the nanoparticle is measured using the data obtained from line profiles on the interfacial region and the size was found to be in the range of 50–90 nm. The attainment of nano particles’ size was confirmed by the Atomic Force Microscope histograms (fig c) and the appearance of clear peak around 60.
75 nm in confirms the existence of maximum number of nanoparticle.TG- DTA TechniqueThermo Gravimetric /Differential Thermal Analysis (TGA/DTA) measurements were obtained using Simultaneous DTA- TGA Apparatus, (DTG- 60, Shimatzu- Japan). The small amount ~ 1 wt% of TGT was placed in the platinum thermo balance crucible for analysis. The samples were heated from room temperature to 900°C, at a heating rate of 20°C/min; the measures were carried out in a constant Air atmosphere.Batch Studies- Aqueous Solutions and Industrial EffluentsBatch equilibration experiments were verified for the operating factors viz., doses of TGT/ NTGT (50-200 mg : 50 mg), agitation time intervals (5- 20min: 5min) at optimized initial metal ion concentration (250mg/L), pH (5.5) and temperature (303K).
The efficiencies of the nano particles were also tested with effluent sample Ni(II)- 220 mg/L collected from electroplating industry at Coimbatore. After the contact period, the supernatant was filtered and the initial and residual Ni(II) ion concentrations were recorded using Atomic Absorption Spectrophotometer (Shimadzu AA 6200) at a wavelength of 283 nm. The percentage values and the amounts of metal ion adsorbed from aqueous solutions were calculated using the equation, % adsorption = (Ci – Ce) / Ci ? 100 and q = V (Ci – Ce) / W respectively V – volume of the solution (L), m – mass of the adsorbent (g), Ci / Ce – initial / equilibrium metal concentrations (mg/L).Results and DiscussionAFM provides us microscopic information on the surface structure and plots the surface topography of the adsorbent. Fig 1(a), 1(b) shows 2D / 3D AFM images from sorbent surface and fig 1(c) clear cut the size of the nano material. NTGT tended to aggregate, thus contributing to some bright areas in AFM height images.
According to fig. 1(c), the grain size of crushed sample is 60.75 nm. The color range shows the morphological changes of the surface, which indicate the adsorption sites on surface of nano TGT.