March 11, 2021
Low-cost adsorbents for water purification
Department of Chemistry
Mississippi State University
Thursday, March 11, 2021
Globally, ~780 million people lack access to pure water because of world population growth, urbanization, and agricultural development. Discharge of heavy metals and other toxic metals, dyes, pharmaceutical products, and oxyanions (PO43-, NO3-) from various point (e.g., wastewater treatment plants), and non-point sources (e.g., runoff) into natural waters deteriorates the physical, chemical, and biological characteristics of water impacting man and aquatic life. Traditional pollutant removal methods such as reduction, flotation, coagulation, flocculation, and membrane filtration have many drawbacks, including initial investment, chemical consumption, efficiency, simplicity, and scalability. Adsorption is a versatile, easy to operate, effective, and economic technique that has been utilized to remove a wide variety of contaminants from wastewater. Owing to their unique and tunable structural, physical, and chemical properties, biochar and lignite-based adsorbents have exhibited great potentials in water treatment.
In the first study, we synthesized three types of pinewood biochar-graphene composites containing three different graphene precursors and compared their aqueous Cu2+ removal performances against raw pinewood biochar. Pre- and post- Cu2+ adsorption behavior of graphene-modified and non-modified biochars and the neat graphenes were characterized by BET, TGA, IR-ATR, XRD, XPS, SEM, TEM, and EDX analysis. In the second study, we engineered a cheap lignite system with co-precipitated Ca2+/Mg2+ followed by pyrolysis at 600 ⁰C to remediate aqueous phosphates. Micro-sized surface deposited oxide/hydroxide/carbonate particles promoted its phosphate uptake by 31 and 72 times, compared to thermally treated lignite (w/o a chemical treatment) and the raw lignite, respectively. The exhausted adsorbent was effectively regenerated in HCl. It could also utilize as a slow-release phosphate fertilizer. In the third study, we synthesized activated lignite, calcium-modified lignite, and iron oxide-modified activated lignite for phosphate removal. Exceptionally high phosphate uptake of calcium-modified lignite was due to the high percentages of surface deposited CaCO3, CaO, and Ca(OH)2. Precipitation of Ca2+ phosphates/hydrophosphates is its major phosphate removal mechanism. Fe3O4 dominates in iron oxide-modified activated lignite and its phosphate adsorption was 8 times greater than its precursor, A-L. Iron oxide-modified activated lignite remediated phosphates mainly via inner-sphere surface complexation and precipitation.