Current World Environment

Introduction

The tremendous increase in the use of heavy metals over the past few decades has inevitably resulted in an increased influex of metallic substances in aquatic environment (Harrison and Laxen 1980). Heavy metal pollution in the aquatic environment is a major health problem. This is because metals are toxic and non-biodegradable (Corapciogie and Hana 1987). Despite the toxicological effects of Cadium, it has a wide range of uses. The most significant use of cadmium is in the Ni-Cd batteries which are rechargeable. The batteries exhibit high output, long life, low maintenance and high tolerance to physical and electrical stress (Hoale 1978). Other uses of cadmium includes, metal coatings, pigments, stabilizers for pVC, in allays and ectropleting. It can also be employed in photo cells, photometry for ultraviolet sun-ray, filaments for incandescent high, electrodes and in denistry as an amalgam. (Okumen and Esther and David 1999). Similarly, lead has wide range uses. It is used in storage batteries, allays, solder, ceramics and plastic. Applied in petrol refining, halogenation, extraction, sulphoneation, manufacture of pigments, insulation cables and wiring household, printing inks glass, textiles and so on (Robert and Rowland). It is also toxic. These metals find their way into the aquatic environment through wastewater discharge (Gurper et al 2003). Because they are non-biodegradable, they tend to accumulate in aquatic organisms. Feeding in such aquatic organisms as fish, crabs or using such contaminated water can lead to metal poisoning in man. Heavy metals pose health hazards, if their concentrations exists the allowable limits. Even when the limits are not exceeded, there is still the potentials of a long term poisoning, since they are known to accumulate within biological systems (Quick, Wase and Fuster 1998). The increasing awareness of the environmental consequences arising from heavy metal accumulation of aquatic environment has lead to the demand for the treatment of industrial waterwater before discharge into aquatic environment.

Conventional treatment processes for metal contaminated wastewater include ion-exchange, chemical precipitation, ultra-filteration, electrochemical deposition and carbon adsorption. These methods though effective are not economically feasible for small and medium scale industries, because of the relatively high costs (Cheremshoff P. and Elizabeth 1979), Lelvani, Hubner, Weston and Matadrich 1998). Hence the need to explore cost effective alternative methods of adsorbants for the treatment of metals contaminated wastewater. There are some readily available waste materials, that posses potentials of cheap adsorbents for the treatment of metal contaminated wastewater. A number of workers have investigated such materials like melon seed husks, maize cob, groundnut husk and oil-palm fibre (Okamen Onyekpa 1989; Okeimen and Okunodye 1989; Okamen Okwuadia Okafor 1991; and Rowl, Lee and Leen 1993). There is still the need to investigate the adsorptive potentials of other cheap and readily available materials that may constitute the class of waste products in the environment. This present work is aimed at examining the potentials of activated and unactivated waste tyre in the removal of (adsorbent) of cadmium and lead from their aqueous solution.
 

Table 1: Variation in adsorptivity of 2g waste tyre powder at different particle sizes Click here to view table

Material and Methods

Waste tyre used in this work was a Michelin brand, collected from a vulcanizer in Onitsha, Nigeria. The tyre was sliced into bits, the metal-threading removal, while the sliced tyres was washed thoroughly with detergent and rinsed severally with clean water to remove any residue. The washed tyre was allowed to dry under the sun.

The dry waste tyre was then ground to powder using a crushing machine. The powder was sieved using the electrical vibration shaker to obtain particle sizes of 500µm, 250µm and 125µm.
 

Table 2: Variation in adsorptivity of 3g waste tyre powder at different particle sizes Click here to view table

The resulting waste tyre powder were subjected to chemical activation. Using hdrocloric acid. The activation process was carried out by mixing a known weight (1g, 2g, 3g & 5g) of waste tyre powder with a known volume of 1mHcl as the activating agent in a ratio of 20cm³ of 1MHCL to 250g of waste powder / Baks, Soumitra and Mahaja 1999), in an evaporating dish. The sample was allowed to dry at room temperature. Various masses of 1g, 2g, 3g and 5g for each of the three particle sizes were weighed and kept in a polyethylene away from moisture.
 

Table 3: Variation in adsorptivity of 5g waste tyre powder at different particle sizes Click here to view table

The varying particle sizes of 500µm, 250µm and 123µm for activated and unactivated waste tyre powder were weighed out in 1g, 2g, 3g and 5g samples and were packed properly into different burettes and exactly 10mls of 20mg/l of standard Pb (NO₃)₂ and allowed for a contact period of 30m minus, for adsorption to take place. The burette tap was then opened after 30 minus and the solution was allowed to drain slowly and the eluent collected and labeled properly. This procedure was repeated for Cd (NO₃)₂. 4H₂O standard solution (30mg/L). The eluent and the stock solution were assayed for metal ions (Pb²⁺ and Cd²⁺) left in the solution using the Atomic Absorption Spectrophotometer with air acetylene flame of 2600⁰C at a measurement time of 4 seconds.

Table 4: Percentage of Pb & Cd metal conc. Adsorbed by activated and unactivated waste tyre powder Click here to view table

Table 5: Variation of mass of adsorbent with adsoptivity of pb2+ and cd2+ at 125μm particle size Click here to view table

Table 6: Variation of mass of adsorbent with adsoptivity of pb2+ and cd2+ at 250μm particle size Click here to view table

Table 7: Variation of mass of adsorbent with adsoptivity of pb2+ and cd2+ at 500μm particle size Click here to view table