Adsorptive removal of Cu(II) by pistachio shell: Isotherm study, kinetic modelling and scale-up designing — continuous mode

Highlights

• Natural pistachio shell was used for Cu(II) from aqueous solution and industrial effluent.

• Study reveals that pistachio shell has adsorptive capacity (33.25 mg/g) for Cu(II) ions.

• Influence of operating parameters were studied.

• Thomas model gives the best illustration of breakthrough curve.

• Scale-up design and treatment of industrial effluent suggests the applicability in real life.

Abstract

Cu(II) ions discharged from various industrial effluents, cause water pollution. Recently adsorption using various low-cost green adsorbents in continuous mode was practised for the mitigation of water pollution. Adsorption of Cu(II) using pistachio shell in continuous lab scale adsorption column was done in this study. Physical characterization of pistachio shell was done by Point of zero charge (pH${}_{\mathrm{pzc}}$) estimation, Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and Brunauer–Emmett–Teller (BET) analysis. Various experiments were done to know the behaviour of adsorption breakthrough against different operating conditions. Langmuir isotherm and Freundlich isotherm were fitted with adsorption equilibrium data, among which fitting of Langmuir isotherm is better ($K_L=0$.4423L/mg, ${\mathit{R}}^2=0$.9986). Seven mathematical models were tried on the experimental result, among them Thomas model performed well for the selected operating range ($k_{TH}=0.636$ mL/(mg. Min), $q_0=12.58$ mg/g, ${\mathit{R}}^2=0$.9431) and utilized for plant designing purpose. Regeneration of pistachio shell with 0.4(N) HCl solution suggests that pistachio shell was able to remove Cu(II) ions multiple time. Experiments using industrial wastewater were also reported. This study signifies that pistachio shell may be utilized for Cu(II) ion removal from industrial effluent.

Introduction

Discharge of toxic heavy metals into our nature causes severe harm (Han et al., 2006, Bishnoi et al., 2004). Different plant operation generates heavy metal bearing wastes and discharge of these wastes causes various damages to the living beings. Cu(II) ion is a well-known heavy metal, comes from different industrial plants like petroleum, electroplating, refining, mining, metal plating, smelting and (Cu-based) agrichemicals etc. (Ahmari et al., 2015, Singha and Das, 2013). Reported health damages caused from uptake of Cu(II) ions are mucosal irritation, gastrointestinal problems, renal impairment, depression and kidney damage etc. (Misra et al., 2013, Altun and Pehlivan, 2007). Inhalation of copper containing sprays causes lung cancer (Bhattacharyya and Gupta, 2011, Larous et al., 2005). Discharge limit of Cu(II) in the industrial effluent is 3.0 mg/L as per CPCB, Govt. of the India (The Environment (Protection) Rule 1986, Schedule VI). Acceptable limit of Cu(II) is 1.5 mg/L in drinkable water as listed in Indian Standards for Drinking water (IS10500:2012) and as per WHO, 2.0 mg/L (Misra et al., 2013).

Various conventional methods were practised for the removal of heavy metals but several difficulties like low removal efficiency, requirements of costly reagents, requirements of sophisticated monitoring system and disposal problem of toxic sludge limits their application (Nag et al., 2017). Adsorption process is found to be very effective against these difficulties, it has a strong affinity toward metal ions and it is simple to use. Various kinds of low cost adsorbents are available which makes adsorption process cheaper than others (Singha and Das, 2013, Al-Othman et al., 2012, Malkoc et al., 2006, Han et al., 2006, Bishnoi et al., 2004). Nowadays different by-products and wastes of agriculture are used for heavy metal adsorption because of their easy availability and low price (Papadimitriou et al., 2017, Ali et al., 2016, Lopez-Nuñez et al., 2014, Hasfalina et al., 2012, Bhattacharya et al., 2008). Usage of agricultural residues for removal process adds some significance to them. Adsorbents as available without any kind of treatment referred to as green adsorbent which has the potential of metal ion removal (Kyza and Kostoglou, 2014).

Large number of works on adsorption process using different adsorbents in batch mode was reported but these were inadequate for industrial process scale-up. For industrial application, a continuous mode of study is required. Continuous study using a fixed bed column gives the best use of driving force, efficient utilization of adsorptive capacity and provides better quality effluent (Salmani et al., 2013). Continuous study facilitates the identification of process difficulties and the performance of adsorbents in the long run. It also gives a prior estimation of fixed as well as operating cost. It is a miniature form of industrial adsorption column and it provides the insight of the process.

Production of pistachio worldwide is around 586,200 MT (shell basis) in 2017–18 and consumption is about 669,860 MT (shell basis) in 2016. Consumption of pistachio in India is around 8042 MT (shell basis) as per the statistical yearbook of nuts and dried fruits (Statistical yearbook, 2017-2018). Shells of pistachio weigh almost 47% of their total weight and generally this vast amount of removed pistachio shells are dumped as solid waste. Many researchers used pistachio shell as the adsorbent for heavy metal removal (Hamidpour et al., 2018, Banerjee et al., 2018a, Aghajani et al., 2014, Turan and Mesci, 2011).

So considering previous studies, pistachio shell was utilized as green adsorbent for Cu(II) removal from aqueous solution in fixed-bed column. Influence of different operating parameters like different influent rate, various bed depth and different influent concentration on adsorption were investigated to identify optimum condition of the process. Two isotherm models Langmuir and Freundlich were applied to the obtained result to verify their applicability for illustration of equilibrium condition. Proper forecasting of process breakthrough curves is needed for designing of the column accurately (Kafshgari et al., 2013). Seven kinetic models like Clark, Wolborska, Yan et al. Bohart–Adams, Yoon–Nelson, Thomas and modified dose response were applied on the obtained result for the investigation of process breakthrough curve and best model which will be further used for designing. Saturated adsorbent was regenerated to ensure its reusability which in turn reduces the cost of adsorbent. Adsorption column scale-up designing was done for small-scale industries and reported in this study. Pistachio shell was used for the treatment of industrial effluent to check its performance against real life effluent.