Synthesis of precipitated calcium carbonate using calcium carbide waste for acid mine drainage remediation

• Main Author: Lye, Xin Yan
• Format: Final Year Project / Dissertation / Thesis
• Published: 2019
• Subjects: TD Environmental technology. Sanitary engineering
• Online Access: http://eprints.utar.edu.my/3939/1/fyp_EV_2019_LXY.pdf; http://eprints.utar.edu.my/3939/

Calcium carbide sludge represents a by-product of acetylene gas production in which this waste material is converted to yield precipitated calcium carbonate (PCC) via surfactantpolymer template precipitation method. In this present study, the synthesized PCC products were employed for the remediation of acid mine drainage (AMD) which manifested a major concern to the environment as a potent surface and ground water contamination due to its high acidity, concentration of dissolved heavy metal ions and anions. The PCC synthesized by hexadecyltrimethylammonium bromide (CTAB), Pluronics® P-123/CTAB (P123/CTAB), polyethylene glycol/CTAB (PEG/CTAB) and polyvinyl alcohol/CTAB (PVA/CTAB) surfactant-polymer templates were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer, Emmett and Teller (BET) surface area and Particle Size Distribution (PSD) analyses. It was demonstrated that the synthesized PCC consisted primarily of high thermodynamically stable calcite with high crystallinity and the presence of C=O and OH bonds. Additionally, BET surface areas of PCC products were determined to range from 8.2487 m2/g to 25.0417 m2/g and were defined as macroporous with pore size of more than 50 nm. PCC products exhibited a uniform mean particle size of 0.158 µm with a narrow size distribution of 0.046 – 0.316 µm. The neutralizing capacity of PCC synthesized by various surfactant-polymer templates was evaluated in terms of pH, oxidative reductive potential (ORP), conductivity and removal of heavy metal ions as well as anions. As a result, the final pH readings of all PCC products complied with national (Department of Environment (DOE) National Water Quality Standards (NWQS) for Malaysia Class IIA as well as Standards A and B of Environmental Quality Act 1974 (EQA) Environmental Quality (Industrial Effluent) Regulations 2009) and international (World Health Organization (WHO) Guidelines for Drinking Water Quality and United States Environmental Protection Agency (EPA) Ore Mining and Dressing Effluent Guidelines 1975 for Iron Ore) standards and guidelines. The PCC synthesized by P123/CTAB was selected as the optimum surfactant-polymer templates due to its achievement of highest pH of 8.22 within standard compliances, lowest ORP of -60.4 mV, highest conductivity of 238.4 µS, high removal efficiency of 87.63 % Al and other heavy metal ions as well as 68.39 % of SO42- ion. In the findings for PCC dosage tests, PCC synthesized by P123/CTAB template with a dosage of 0.40 g/L attained a final pH of 8.36, ORP of -61.4 mV and conductivity of 230.1 µS with a removal efficiency of 32.52 % for Mn and 72.77 % for SO42- ions. It represented the optimum dosage due to its close proximity with the high neutralizing performance of 0.50 g/L dosage, yet would be more economical for use in large-scaled treatment of AMD. For sludge settling, PCC synthesized by P123/CTAB template of 0.40 g/L dosage successfully acted as a weighing material to precipitate heavy metal and SO42- ions in AMD.