Enhanced Adsorption Capacity and Selectivity toward Inorganic and Organic Mercury Ions from Aqueous Solution by Dye-Affinity Adsorbents Norasikin Saman, a Khairiraihanna Johari, b Shiow-Tien Song, a Helen Kong, c Siew-Chin Cheu, a and Hanapi Mat a,d a Advanced Materials and Process Engineering Laboratory, Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia b Department of Chemical Engineering, Faculty of Engineering, Universiti Teknologi PETRONAS, 32610, Bandar Seri Iskandar, Perak, Malaysia c Centre of Lipid Engineering and Applied Research, Level 2 C08, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia d Advanced Materials and Separation Technologies (AMSET) Research Group, Health and Wellness Research Alliance, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia Published online 00 Month 2018 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.12915 Adsorption of inorganic mercury [Hg(II)] and organic methylmercury [MeHg(II)] ions onto dye-affinity agrowaste (dye-AW) was investigated. The dye-affinity adsorbents were prepared by the chemical-thermal reaction between the agro- waste (AW) and dye solutions [i.e., Reactive Red 120 (RR), Reactive Black B (RB), Methylene Blue (MB), and Methyl Orange (MO)] under an alkaline condition. An almost per- fect removal of Hg(II) was observed for all adsorbents, while for MeHg(II), the dye-affinity adsorbents have a higher removal efficiency than a pristine adsorbent. The maximum adsorption capacity (Q e, max ) of mercury ions onto the Reac- tive Red 120-modified AW (RR-AW) was 2.60 mmol g 21 for Hg(II) and 0.76 mmol g 21 for MeHg(II). The adsorption rate of Hg(II) was faster than MeHg(II), and both kinetic data fol- lowed the pseudo-second order kinetic model with the diffu- sion steps controlled by the film diffusion. The regenerated adsorbent showed very encouraging results especially toward Hg(II). The promising results were also obtained by using oil- field produced water (OPW) and natural gas condensate (NGC) samples. These studies finally demonstrated that the agricultural wastes initially loaded with dyes have the poten- tial to be good mercury adsorbents. V C 2018 American Institute of Chemical Engineers Environ Prog, 00: 000–000, 2018 Keywords: adsorption, agricultural wastes, dye, mercury INTRODUCTION The usage of heavy metals in the process and manufactur- ing industries has led to several major environmental prob- lems. Among the heavy metals, mercury has drawn much attention due to its toxicity. A release of mercury even at a very small amount can result in a significant threat to the ecological system and human health [1,2]. Coal and munici- pal waste combustions, gold mining, oil and gas production and processing, and cement production are the main anthro- pogenic sources of the mercury releases [3]. These activities release various forms of mercury such as elemental, inor- ganic, and organic mercury. Organic methylmercury is known as the most toxic mercury form because it can be easily bioaccumulated in the human food chain. More impor- tantly, the inorganic mercury can be easily transformed into more toxic organic mercury forms due to the presence of microbial activity [2,4]. Preventing or reducing the release of mercury into the environment is thus very crucial. There are many technologies presently employed for removing mercury ions in various effluents. Out of the numerous technologies, adsorption in particular is a promis- ing technology for the selective mercury removal processes. However, the conventional activated carbons as adsorbents are quite expensive due to their high cost of production. Therefore, there is always a need for designing new adsorb- ents that can capture mercury with a high adsorption capac- ity and selectivity as well as cheaper. Many studies have been conducted using low-cost materials such as agrowastes [5–8], sewage sludge carbon [9], industrial wastes [10,11], peats and soils [12] for removing mercury ions from aqueous solutions and wastewaters. Several chemical modifications [8,13–17] and thermochemical processes [18–20] have been performed to increase the adsorption performance of the pristine adsorbents. The surface treatment by the introduction of dye ligands on the adsorbent surfaces to enhance their surface affinity toward target adsorbates has been widely studied for protein separation [21] and less studied for other adsorbates such as heavy metals [22–25]. A number of textile dyes, known as reactive dyes have been used in dye-ligand affinity systems for protein separation [26–29], and heavy metal adsorption V C 2018 American Institute of Chemical Engineers Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep Month 2018 1 Published online 4 May 2018 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.12915 tial to be good mercury adsorbents. © 2018 American Institute of Chemical Engineers Environ Prog, 38: S54–S67, 2019 S54 March 2019 Environmental Progress & Sustainable Energy (Vol.38, No.S1) DOI 10.1002/ep