Evaluation of the efficiency of okra adsorbent for heavy metals removal from wastewater in natural gas production

Abstract

Nowadays, one of the leading environmental pollutants is heavy metals. This is due to the rapid development of industry and the over-exploitation of natural resources in many countries. Hence, heavy metals in wastewater must be removed before discharge because they are toxic even at low concentrations. This research aims to evaluate the efficiency of okra waste as an adsorbent for heavy metals removal from wastewater in natural gas production. The FTIR was used to characterize the okra-activated carbon and the peaks showed the presence of functional groups such as Hydroxyl (OH), Amino (N-H), Carboxyl (C=O, C-O-C), C-0 stretching and M-O. Furthermore, the batch adsorption experiments were conducted via varying agitation speed, contact time, adsorbent dose and adsorbent particle sizes. After extraction and adsorption batch process, samples were analyzed using Inductively Coupled Plasma-Optical (or atomic) Emission Spectrometry (ICP-OES). The results showed that the maximum removal percent of Cd2+, Cu2+, Pb2¬+, Zn 2+, Ag2+ and Ba2+ metal ions had been observed to be at an agitation speed of 1000 rpm, contact time of 90min¬, okra adsorbent dose of 0.25 g and particle size of 1.00mm. Then, the Langmuir isotherm model was applied to describe the maximum adsorption capacity (Qmax) calculated for Cd (II), Pb (II), Zn(II), Cu(II), Ba(II) and Ag(II) metal ions. The maximum adsorption capacity (Qmax) has been addressed to evaluate the fitting ability of the Langmuir isotherm model, wherever it yielded a better fit to the experimental data with higher correlation coefficients (R2) belongs between (0.888-0.999). Thus, the okra adsorbent showed a very high adsorption capacity for Ba2+ as 64.102 mg/g following for Cu2+ as 14.8 mg/g followed by Pb2¬+, Zn2+, Cd2+ and Ag2+ as 8.37 mg/g 7.09 mg/g, 1.79 mg/g and 0.90 mg/g respectively and the 𝑅𝐿 value in the present study for Cd2+, Cu2+, Pb2¬+, Zn2+, Ag2+ and Ba2+ ions were found to be 0.0003 , 0.0027 , 0.0001 , 0.0002, 0.0002 and 0.2705 respectively . Therefore, all values of RL were less than one, indicated that the adsorption of these heavy metals ions onto okra adsorbent is favorable. The experimental results prove that due to its high efficiency for Cd2+, Cu2+, Pb2¬+, Zn2+, Ag2+ and Ba2+ ions removal from wastewater, okra wastes from agricultural by-products are promised to be used as a low-cost adsorbent for further studies to remove other heavy metals.