Adsorption Characteristics of Spent Coffee Grounds as an Alternative Adsorbent for Cadmium in Solution

Min-Suk Kim,Jeong-Gyu Kim

doi:10.3390/environments7040024

Abstract

The present study was conducted to ascertain the potential of spent coffee grounds (SCGs) as an alternative adsorbent for the removal of cadmium (Cd) from aqueous solutions. Therefore, Cd adsorption batch tests, using SCGs that had not undergone any chemical pretreatment, were conducted using Cd solutions with a wide concentration range (i.e., 0.1–120 mM) under various adsorption conditions, e.g., ion strength, pH, and solid/solution ratio. For comparison, zeolite, as a well-known common representative adsorbent, was included to determine the adsorption efficiency. The adsorption capacity of the SCGs increased with the decreasing ionic strength of the test solution from 200 to 0 mM of Ca(NO3)2 and the increasing solid:solution ratio from 1:4 to 1:400. The most significant factor influencing the adsorption capacity of the SCGs was the pH of the test solution, with increases in the adsorption capacity as the initial solution pH was increased from 2 to 10. However, the rate for Cd removal remained constant, at 71.19%, when the initial solution pH was between 4 and 8 due to the buffer capacity of SCGs. The obtained data were fitted with the Freundlich, Langmuir, and Dubinin-Radushkevich isotherm models. The Langmuir isotherm provided the best correlation for Cd adsorption onto SCGs (R2 = 0.96) and zeolite (R2 = 0.92), and the maximum Cd adsorption capacity of the SCGs was 19.32 mg g-1, which was higher than that of zeolite (13.91 mg g−1). These results mean that the SCGs can be utilized as alternative low-cost biosorbents to replace conventional adsorption materials.

Highlights

Heavy metals, including cadmium, lead, copper, and zinc, have been widely dispersed into the environment by anthropogenic activities, such as mining operations, metal plating, and other industrial activities [1,2]
The spent coffee grounds (SCGs) were rich in organic matter, accounting for 94.65% of the total mass, while zeolite contained only 1.31%
The current study showed that the SCGs without any pretreatment exhibited a higher Cd adsorption capacity and appeared to be a better candidate adsorbent than any other raw agro-waste material for the removal of Cd from solution

Summary

Introduction

Heavy metals, including cadmium, lead, copper, and zinc, have been widely dispersed into the environment by anthropogenic activities, such as mining operations, metal plating, and other industrial activities [1,2]. Various types of techniques have been suggested for reducing heavy metals and their availability in aqua systems, e.g., ion-exchange, osmosis, membrane process, and electrolytic methods; many techniques are costly and may be accompanied by the generation of by-products [5]. Among these various techniques, the removal of heavy metals via their adsorption onto adsorbents has been considered the most versatile, as a relatively simple and cost-effective technique. Activated carbon is one of the most widely adopted adsorbent materials due to its Environments 2020, 7, 24; doi:10.3390/environments7040024 www.mdpi.com/journal/environments

Methods

Results

Conclusion