Application of Mn-Fe Layered Double Hydroxide as an Adsorbent for the Removal of Arsenic from Synthetic Acid Mine Drainage

The Mn-Fe layered double hydroxide using chloride in the interlayer anion was successfully synthesized using chemical co-precipitation methods. The Mn-Fe LDH was then applied as adsorbent for arsenic removal from synthetic acid mine drainage. The adsorbent characterizations of SEM and XRD analysis showed that the Mn-Fe LDH had many different functional groups and a high specific surface area for the adsorption processes. The morphological structure of Mn-Fe LDH by the SEM-EDS analysis method shows a round shape structure with a particle size of about 1 μm, and the XRF analysis method shows that the Mn and Fe elements dominate more than other components. Batch adsorption experimental conducted using the Mn-Fe LDH with the interlayer anion of chloride as an adsorbent to study the effect of contact time, equilibrium pH, and temperature on the arsenic removal. The Mn-Fe LDH showed high adsorption uptake capacity and selectivity for the arsenic in the synthetic acid mine drainage. The adsorption and ion exchange between interlayer chloride anions in Mn-Fe LDH and As (V) solution was the main adsorption mechanism. Therefore, the Mn-Fe LDH can be used as an adsorbent in water and wastewater treatment. In contrast, this research has the potential to be processed and developed into advanced materials.

Iron removal and pH stabilization of synthetic acid mine drainage (AMD) using peat soil and limestone.

A Successive Alkalinity Producing System (SAPS) was evaluated for the remediation of synthetic Acid Mine Drainage (AMD) by using an organic substrate of peat soil and limestone aggregate. The characterization of the AMD was conducted by the testing the AMD effluent originated from active mining site at Pengkalan Hulu, Perak, Malaysia. The characterization of the peat soil and limestone revealed stipulated composition, carbon content in the peat soil and particle size distribution of the limestone. Synthetic AMD was prepared incorporating iron sulphate (FeSO4) and sulphuric acid (H2SO4). The synthetic AMD was acidic (pH < 4.0) and with 50, 75 and 100 ppm Iron (Fe) concentration. A laboratory scale physical model to simulate a tailing pond was developed. The synthetic AMD was introduced and passed through the filtration media. Subsequently, water samples were collected and analyzed to determine pH level. Additionally, the Fe concentration was analyzed using UV-Vis test at 6 to maximum 48 hours’ retention time. The residues of the peat soil and limestone from the physical model were further analyzed using SEM-EDX microscopic to determine the remaining iron content absorb or precipitate onto the peat soil and limestone. The analysis revealed that the innovative methodology has successfully reduced more than 85 % iron content and neutralized the pH only after 6 hours of retention time. These results proved the combination of peat soil and limestone potentially can be proposed as the alternate solution for treating the AMD effluent from the mining site.

Sequential Abatement of FeII and CrVI Water Pollution by Use of Walnut Shell-Based Adsorbents

In this study walnut shells, an inexpensive and readily available waste, were used as carbonaceous precursor for preparation of an innovative adsorbent (walnut-shell powder (WSP)) which was successfully tested for the removal of FeII from synthetic acid mine drainage (AMD). Then, the exhausted iron-contaminated adsorbent (WSP-FeII) was recovered and treated with sodium borohydride for the reduction of adsorbed FeII to Fe0. The resulting material (WSP-Fe0) was subsequently tested for the removal of CrVI from aqueous solutions. Treatability batch experiments were employed for both FeII and CrVI-contaminated solutions, and the influence of some important experimental parameters was studied. In addition, the experimental data was interpreted by applying three kinetic models and the mechanism of heavy metal removal was discussed. The overall data presented in this study indicated that fresh WSP and WSP-Fe0 can be considered as promising materials for the removal of FeII and CrVI, respectively. Furthermore, the present work clearly showed that water treatment residuals may be converted in upgraded materials, which can be successfully applied in subsequent water treatment processes. This is an example of sustainable and environmentally-friendly solution that may reduce the adverse effects associated with wastes and delay expensive disposal methods such as landfilling or incineration.