Super adsorbent - based remediation and on-site flow injection analysis determeniation of arsenic ions in gold mining site

Abstract

Arsenic is a mineral which is abundant in gold mining sites. It is a toxic substance which needs to be removed. Thus, this research investigated the problem of extremely high arsenic (As) concentration in effluent (water and slurry) from Selinsing gold mine site, Pahang, Malaysia and developed an effective operational remedial method using an adsorbent material (Ecomel). In this research, a new method for measuring As(III) and As(V), which exist in the contaminated soil and liquid effluents was developed using flow injection analysis (FIA) system, while the total As was analyzed using atomic fluorescence spectrometry (AFS) for the remediating samples. By using the FIA method, the As speciation detection limit of (S/N = 3) for both As(III) and As(V) were found to be 5 μg/L with standard deviation 2.2 (n = 20). It also showed a wide dynamic range coefficient of detection (R2) of 0.999 for As(III) and 0.9989 for As(V). This portable analytical method was successfully applied for the determination of As speciation in the effluent collected from Selinsing gold mine site without further treatment. For the characterizations of slurry and adsorbent materials (Ecomel), X-ray diffraction (XRD), X-ray fluorescence (XRF), energy-dispersive X-ray spectroscopy (EDX), Field Emission Scanning Electron Microscopy (FESEM), Focus Ion Beam–Scanning Electron Microscope (FIB-SEM), Inductively Coupled Plasma Optical Emission Spectrophotometer (ICPOES), Elemental Analyzer (EA) and Brunauer–Emmett– Teller (BET) were used. In the case of liquid effluent from the tailing dam, the pH and cyanide concentrations were measured at 11.5 and 204 mg/L, respectively. However, the batch experiments clearly proved that As leaching from the slurry (contact time: 24 h, stirring speed: 200 rpm, and S:L ratio 1:5) was extremely higher at pH 11.5 compared to pH 2.5 and were measured to be 8,720 and 1,010 μg/L, respectively. The major contributors to the exceedingly elevated levels of As concentration in liquid effluents were attributed to alkaline pH, high cyanide and silicate concentration, as well as high oxidation environment. The batch experiments on Ecomel revealed that maximum adsorption capacity determined at initial pH 2.5 from the Langmuir-Freundlich isotherm model was found to be 704.7 and 122.7 mg/g for As(III) and As(V), respectively. These results indicated that Ecomel has high adsorbent efficiency, cost-effective and is suitable for in-situ and ex-situ remediation of highly concentrated As(III) and As(V) toxicants in aqueous solutions. For As standard solution with initial pH 2.5 and concentration of As at 1 mg/L, it was observed that 0.3125 g/L of Ecomel with 2 h contact time can adequately remove 97.0% of As(V) and 98.1% of As(III), respectively. As a conclusion, results from AFS showed that the treatment of As using Ecomel at initial pH 2.5 was the most proficient for remediation of liquid effluent and slurry.