Copper Recovery from Aqueous Solutions by Hemp Shives: Adsorption Studies and Modeling

Abstract

This article describes the performance of hemp shives, a co-product of the hemp industry, when used as an adsorbent to recover copper present in aqueous solutions by a batch method. Two materials provided by an industrial partner, namely water-washed hemp shives (SHI-W) and Na2CO3-activated shives (SHI-C), were studied. Two important variables in the water treatment industry, i.e., pH and ionic strength of the solution, were studied to evaluate their impact on the purification performance of the materials. The results obtained clearly indicated that the performance in terms of Cu removal obtained from the SHI-C material was significantly higher than that obtained with SHI-W, mainly due to the structural and chemical modifications after carbonate treatment. For each dose of this adsorbent, a percentage of recovery between 90 and 100% was achieved, independently of the pH value in the range 3–5. In the case of SHI-W, the highest values were between 60 and 75% and were both dependent on the pH and the dose used. SHI-C was also able to selectively remove 70% of copper in the presence of NaCl 1M. The analysis of the isotherms indicated the presence of a complex adsorption mechanism that cannot be described by only one isotherm model.

A Strategy to Valorize a By-Product of Pine Wood (Pinus pinaster) for Copper Removal from Aqueous Solutions

“…Experimental kinetic data were modeled using various empirical models commonly used in the literature [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. The graphical representations of these models are shown in Figure 4 , and the calculated parameters are presented in Table 1 .…”

“…However, a full analysis of the modeling via these Weber and Morris and Elovich models has shown that neither of these two models is entirely satisfactory in describing all the kinetic data for copper adsorption on maritime pine. The mechanism is far more complex than simple physisorption, chemisorption and/or diffusion [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. Indeed, lignocellulosic materials such as those in this work are known to have a complex structure, with fibers consisting of tangles of cellulose microfibrils covered with hemicellulose and lignin in the outer layer, as well as fiber anatomy with a more or less accessible lumen.…”

“…They suggested that, due to these interactions and ignoring concentration values, the heat of adsorption of all adsorbates in the layer would decrease linearly with coverage. This concept is expressed by the so-called Temkin Equation (9), in which K T is the equilibrium binding constant (L/g) corresponding to the maximum binding energy and B is another constant (J/mol) related to the adsorption energy [ 46 , 49 ].…”

“…The analytical technique used to determine the purification performance of wood samples is the so-called batch technique [ 46 ], which involves bringing a given mass of material into contact with a volume of solution to be treated under pre-defined experimental conditions. The mixture is then stirred for a certain period of time and filtered.…”

“…The experimental results for kinetics and adsorption, in a ternary adsorbent/adsorbent/water system, can be modeled by simple, empirical, two-, three- or n-dimensional equations [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ]. For kinetic results, the models of Lagergren (Equation (3)) [ 54 ], Ho and McKay (Equation (4)) [ 55 ], Weber and Morris (Equation (5)) [ 56 ], and Elovich (Equation (6)) [ 57 ] were chosen, and for adsorption data, the adsorption isotherms of Langmuir (Equation (7)) [ 58 ], Freundlich (Equation (8)) [ 59 ], and Temkin (Equation (9)) [ 60 ] were selected.…”