Adsorption of heavy metals from mine wastewater using amino-acid modified Montmorillonite

ABSTRACT

This study was conducted to identify the ability of a modern developed amino-acid modified montmorillonite clay (AA-Mont) to adsorb Cu²⁺, Pb²⁺ and Ni²⁺ cations from a multi-aqueous wastewater. This experimental was conducted to identify the potential of clay-based adsorbents to remediate pollutants from the PRA river basin. Experimental wastewater was prepared using a range of the lowest and highest recorded upstream and downstream heavy metal concentrations of u²⁺(10.84 mg/L-108.48 mg/g), Ni²⁺(7.99 mg/g–79.92 mg/g), and Pb²⁺(33.538 mg/L—335.38 mg/L). The variants of the designed clay-based adsorbents were L-Cysteine montmorillonites (Cys-Mont), Glycine montmorillonite (Gly-Mont), and L-lysine Montmorillonites (Lys-Mont) prepared at pH 4, 5, and 6 respectively. The experimental conditions were; Adsorbent dosages range = 25 mg–400 mg, pH = 6.0, Contact time = 24 hrs, Temperature = 25°C and Shaker speed = 180 rmp. After the adsorption experiments, it was identified that the maximum average removal efficiency obtained for Cu²⁺, Ni²⁺, and Pb²⁺ were all attained at adsorbent dosage 400 mg/L and in the order Lys-Mont (99.82%)>Cys-Mont (99.28%)>Gly-Mont (95.8%). Thus, the modified Lys-Mont clay exhibited the highest heavy metal adsorption capacity amongst the above three studied. The highest and lowest adsorbed metal pollutants amounts recorded for Lys-Mont were Cu²⁺ (86.49 and 8.65) mg/g, Ni²⁺ (44.51 and 5.99) mg/g, and Pb²⁺ (267.85 and 26.67) mg/g respectively. The number of metal ions adsorbed per unit mass for each metal cation tested decreased with increasing adsorbent dosage. The general order of selectivity documented for all the AA-Monts in this study was Pb>Cu>Ni which is similar to the levels in the prepared wastewater solution (Pb>Cu>Ni). The findings of this study have shown that heavy metal polluted river basins can remediated given the right conditions of temperature, adsorbent dosage, pH and agitation speed.

Graphical abstract

KEYWORDS:

• Adsorption
• montmorillonite
• Heavy Metals
• Lysine
• Glycine
• Cysteine

Public interest statement

Ghana with its rich natural resources has significantly benefited from the exploitation of gold. By January 2016, gold mining contributed ~5.7% and ~40% to its GDP and gross foreign exchange earnings. Notwithstanding these notable gains, gold mining in Ghana continues to harm the environment, human health, and the long-term sustenance of community livelihoods.

In this research study, heavy metals (Cu²⁺, Ni²⁺ & Pb²⁺) associated with Ghana’s illegal gold mining (Galamsey) were adsorbed from a multi-aqueous wastewater solution using a variety of novel amino-acid modified montmorillonite clay absorbents. The best performing absorbent was Lysine montmorillonite (Lys-Mont) with a removal efficiency of 99.82% at an adsorbent dosage of 400 mg/L, pH (6), Temperature (25°C), contact time (24 hrs) and agitation speed (180rmp). This result indicates the possibility of remediating mining polluted rivers with eco-friendly, green, and inexpensive adsorbents. This is a good step in ensuring sustainable gold mining in developing countries.

Limitations of the Study

This study used a contact reaction time of 24 hours (assumed reaction time to reach equilibrium). Therefore, the major limitation of the study was that no isotherm or adsorption kinetics was studied. When the Pseudo first or second order studies was also not discussed. However, further studies will be conducted in future research to address these limitations

Availability of data and materials

The dataset generated and/or analyzed during the current study is available from the corresponding author on reasonable request.

Acknowledgements

The authors are grateful to God for the opportunity given them to materialize their study and to the South West University of Science and Technology – China for the opportunity to conduct all experiments in their laboratory. Also, we appreciate all team members and individuals (especially Professor Liang Bian) who in one way or the other contributed greatly to the success of the study. Thank you and my God bless you all.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Christiana Boahen: Conceptualized the research topic, and developed the objectives and methodology of the research.

Samuel Wiafe: He carried out both the Laboratory and Field Investigation as well as the Data Curation of the research work

Fredrick Owusu: He carried out Laboratory work and assisted in the writing of the manuscript.

Liang Bian: He participated in the Writing of the manuscript (Original Draft Preparation) as well as reviewed and edited the manuscript.

Additional information

Funding

This study was wholly funded by the authors of this research.