Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Humic acid coated cellulose derived from rice husk: A novel biosorbent for the removal of Ni and Cr Hirakendu Basu, Sudeshna Saha, Iyer Akshara Mahadevan, Mehzabin Vivek Pimple, Rakesh Kumar Singhal ⁎ Analytical Chemistry Division, Bhabha Atomic Research Center, Trombay, Mumbai, 400085, India ARTICLE INFO Keywords: Biosorption Humic acid Cellulose Soda bleaching Sorption isotherms ABSTRACT Biosorption using cellulosic wastes has been considered as a clean technology for the uptake of heavy metals. In this study, a novel biosorbent was synthesized by extracting the cellulose from the waste rice husk using soda bleaching technique followed by its coating using humic acid. The biosorbent was found to be very effective for the removal of nickel and chromium from the aquatic medium. Various physicochemical conditions for uptake like pH (5–6), contact time (8 h) were optimized using batch method.The sorption capacity enhanced sig- nificantly by providing humic acid coating. Experiment data were fitted in sorption isotherm and kinetic modelstodescribe the sorption process.Sorption capacity of developed biosorbent was 12.41 mg g -1 and 19.39 mg g -1 for nickel and chromium respectively and the sorption followed the Langmuir isotherm for both the elements. 1. Introduction Heavy metal pollution in the aquatic streams is an ever-increasing environmental concern. The major sources of heavy metal pollution are various factories, each releasing a different pollutant in the effluent, corrosion of different components, release from waste disposal facil- itiesetc. [1,2].They are highly hazardous due to their property of being non-biodegradable thus resulting in bioaccumulation in living organ- isms leading to diseases [3,4]. Nickel and chromium are among the few heavy metals that are considered as environmental pollutants because as their toxicities [5,6]. Many nickel salts are easily soluble in water making it more prone to leaching and subsequent water contamination. It is seen that acid rain increases nickel leaching into water. Soil pH, use, sampling depth affect the concentration of nickel in groundwater. Although some amount of nickel is required by the human body, acute nickel toxicity may lead to kidney malfunction and at extremes to cancer. Major source of nickel are metal factories, incinerators, fertili- zers and power plants [7]. Chromium is a colorless metallic element found in rocks, soils, plants and volcanic elements. Being an essential dietary product, it is found in fruits, vegetables, grains and meat. In the environment, chromium is released by the various industries like tan- ning, wood preservation, dyes, chrome plating and various alloy man- ufacturers. It exists as both Cr (II) and Cr (VI) of which the latter is the more dangerous and highly carcinogenic. The maximum permissible level for Cr was set at 0.1 μgmL -1 by the EPA. One of the most common symptoms of chromium poisoning is contact dermatitis [8]. Several chemical agents have been used as sorbents for adsorption of heavy metals. These agents are for most of the time ineffective or uneconomical due to the scale of the operation. This led to the devel- opment of a new class of sorbents using biomass. When the sorbent is of a biological origin, it is termed as a biosorbent [9–12]. Biosorbents can be both living and non-living.It is an active process when a living cell is involved as the metabolic process of the cell leads to sorption. On the other hand, when dead cells or biomass acts as a sorbent, the process is a passive process.Various materials have been used as a biosorbent like: Dried water hyacinth roots, Seaweed, Tea leaves, Yeast biomass, Saw- dust, Olive stones, Fish scales, Soybean hulls, Oil-palm fibres, Moss, Rice hulls, Chitin, Animal bones, Bacteria, Fungi. [13,14].Adsorption of Cr(VI) ions onto various sorbents was reported. For example optimum pH for Cr(VI) adsorption on Chitin and chitosan was found as 3.0 which is very low. For some of the sorbents uptake kinetics was found to very slow [15]. Recently kaolinite [16] and blast furnace slag [17] have been used for Ni uptake from water.Several factors need to be considered during biosorption studies like the cost of metal (usefulness after re- covery), its toxicity and its use in further research.One of the most common adsorbent used is cellulose which is mainly the cell wall structure of the biomass which enable the metal uptake and thus purify water. Cell walls contain several functional groups that bind with https://doi.org/10.1016/j.jwpe.2019.100892 Received 20 March 2019; Received in revised form 7 June 2019; Accepted 5 July 2019 ⁎ Corresponding author. E-mail address: rsinghal@barc.gov.in (R.K. Singhal). Journal of Water Process Engineering 32 (2019) 100892 2214-7144/ © 2019 Elsevier Ltd. All rights reserved. T