COMPARATIVE STUDY ON CONTROLLED STAGED PRECIPITATION OF RARE EARTH ELEMENTS FROM ACID MINE DRAINAGE USING ELECTROCHEMICAL AND CHEMICAL TREATMENT METHODS

Author

• Pratik Southern Illinois University Kushwaha, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2026

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

Fakhraei, Habibollah

Abstract

Acid mine drainage (AMD) is a major environmental concern due to its high acidity and elevated concentrations of dissolved metals. In addition to being an environmental problem, AMD has increasingly attracted attention as a possible secondary source of rare earth elements and yttrium (REY). However, traditional treatment strategies generally focus on bulk metal removal and offer limited control over the selective recovery of individual metals. This study evaluates the staged recovery potential of iron (Fe), aluminum (Al), and REY from AMD collected at the Tab-Simco abandoned coal mine site using electrochemical pH adjustment and compares its performance with conventional chemical neutralization. A bench-scale two chamber electrochemical system equipped with an anion exchange membrane was used to progressively increase pH in stages to pH 4, 5 and 7, enabling controlled metal precipitation. Parallel chemical neutralization experiments were conducted under similar conditions. The concentrations of metals were measured by inductively coupled plasma mass spectrometry (ICP MS), and the geochemical speciation and precipitation of Fe, Al, and REY within the treatment systems were predicted using Visual MINTEQ. Electrochemical impedance spectroscopy (EIS) analysis was conducted to investigate variations in system resistance and interfacial characteristics. The results demonstrated pH-dependent staged removal of metals. In the electrochemical system, near-complete removal (>99%) of Fe, Al, and REY was achieved at pH 7. Aluminum removal occurred predominantly at pH 5 (~98%), followed by progressive removal of Fe and REY at higher pH values. In comparison, chemical neutralization showed relatively lower Fe removal (~69%), while high Al removal at pH 5 (>98%) and significant REY removal at higher pH values were observed. A mass balance analysis revealed that the Fe mass balance closed to a relatively higher extent in the electrochemical system (~92%), whereas chemical treatment showed higher closure for Al (~68%) and REY (~80%), likely due to differences in metal partitioning and recovery mechanisms. From an operational point of view, electrochemical treatment consumed 8.16 Wh for 500 ml of AMD, which translates to a specific energy consumption of 16.3 kWh m-3, whereas chemical neutralization required 1.57 kg NaOH m-3. Overall, the electrochemical system showed effective staged metal recovery with enhanced Fe removal and comparable REY recovery, highlighting its potential as a controlled and sustainable alternative for AMD treatment and resource recovery.