Abstract
Environmentally hazardous pollutants and heavy metals are commonly present in produced water (PW) from oilfields. Most conventional treatment methods are either prohibitively expensive or ineffective at removing heavy metals at low concentrations. This study focused on the adsorptive removal of Pb²⁺ and Ni²⁺ from PW sourced from the Oredo Oil Field in Nigeria, using a blend of three adsorbents: rice husk, banana peels, and orange peels in equal proportions. These adsorbents were dried, crushed, and sieved through a 75 μm mesh screen before being mixed. The adsorbent blend was characterized using Fourier Transform Infrared (FTIR) spectroscopy and Brunauer Emmett Teller (BET) analysis. Batch adsorption experiments were conducted to examine the effects of contact time and adsorbent dosage on heavy metal removal. FTIR analysis identified functional groups such as alkyl, carbonyl, and ether, which suggest effective interaction with lead and nickel ions. BET characterization revealed a specific surface area of 406.55 m²/g, a pore volume of 0.1609 cm³/g, and an average pore size of 3.143 nm. These properties indicate that the adsorbent possesses a high density of active surface sites and mesoporous structure conducive to efficient adsorption of small-sized heavy metal ions such as Pb²⁺ and Ni²⁺. The study found that lead removal reached a maximum of 66% with an adsorbent dosage of 2 g/L after 105 minutes, while nickel removal peaked at 51% with an adsorbent dosage of 0.5 g/L after the same duration. The analysis demonstrated that the adsorbent exhibited notable adsorption properties, with higher affinity and selectivity for Pb compared to Ni. Adsorption kinetics were best described by the pseudo-second-order model for both lead and nickel, while the Freundlich isotherm model was the most suitable for describing the adsorption processes.

Key words: Adsorption, Heavy metals, Isotherms, Kinetics, Produced water