Adsorption of Heavy Metals Ions from Mining Metallurgical Tailings Leachate Using a Shell-Based Adsorbent: Characterization, Kinetics and Isotherm Studies

Abstract

This study defines the optimal parameters that allow the use of waste mollusk shells (WS) to remove heavy metals from three mining and metallurgical leachates. First, the influence of parameters such as pH, contact time, initial metal concentration, adsorbent dose and the presence of co-ions in Cu²⁺, Cd²⁺, Zn²⁺ and Ni²⁺ adsorption was investigated in synthetic solutions. Metal uptake was found to be dependent on the initial pH of the solution, the removal rate increasing with the increase in pH, showing the highest affinity at pH 5-6. The removal efficiency at lower concentrations was greater than at higher values. The competitive adsorption results on bimetallic solutions showed that the adsorption capacity of the sorbent was restricted by the presence of other ions and suppressed the uptake of heavy metals compared to the single adsorption. Cu²⁺ was the metal that most inhibited the removal of Cd²⁺, Zn²⁺ and Ni²⁺. The Langmuir isotherm provided the best fit to the experimental data for Cu²⁺, Cd²⁺ and Zn²⁺ and the Freundlich isotherm, for Ni²⁺. The data showed that the maximum adsorption capacity a_max for Zn²⁺, Cd²⁺ and Cu²⁺, was 526.32 mg g^-1, 555.56 mg g^-1 and 769.23 mg g^-1, respectively. Sorption kinetics data best fit the pseudo-second-order kinetic model. The results obtained in the tests with three mining and metallurgical leachates showed that WS were effective in simultaneously removing several heavy metals ions such as Cu, Ni, Zn, Cd, Ni, As and Se.

Keywords: adsorption; heavy metal; landfill leachate; mollusks’ shell; wastewater treatment.

Figure 1

Thermogravimetric analysis of WS.

Figure 2

XRD diffractogram of WS: A—aragonite and C—calcite.

Figure 3

Scanning electron micrograph and EDAX spectrum of WS.

Figure 4

Metals removal onto WS versus initial pH at different adsorbent concentration: 0.4 g L⁻¹, 4 g L⁻¹ and 10 g L⁻¹. (a) % Ni removal; (b) % Zn removal; (c) % Cd removal; (d) % Cu removal.

Figure 5

Metals removal onto WS versus time at different adsorbent concentration: 0.4 g L⁻¹, 2 g L⁻¹, 4 g L⁻¹ and 10 g L⁻¹. (a) % metal removal at 0.4 g L⁻¹; (b) % metal removal at 2g L⁻¹; (c) % metal removal at 4g L⁻¹; (d) % metal removal at 10 g L⁻¹.

Figure 6

Metals removal onto WS versus initial concentration at different adsorbent concentration: 0.4 g L⁻¹, 2 g L⁻¹, 4 g L⁻¹ and 10 g L⁻¹. (a) % Ni removal; (b) % Zn removal; (c) % Cd removal; (d) % Cu removal.

Figure 7

Scanning electron micrograph and EDX analysis of WS after the treatment of the leachate using an adsorbent concentration of 0.4 g L⁻¹.

Figure 8

X-ray diffraction patterns of WS after treatment. O—otavite, P—posnjakite, M—malachite, H—hydrozincite, X—Ni₅(CO₃)₄(OH)₂·4.5H₂O, Y—Ni₃(CO₃)(OH)₄·4H₂O, A—aragonite and C—calcite.