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Carnallite-Derived Solid Waste as Potassium (K) and Magnesium (Mg) Source in Granulated Compound NPK Fertilizers

Sharma, Lohit, Brigaityte, Odeta, Honer, Kenneth, Kalfaoglu, Eren, Slinksiene, Rasa, Streimikis, Virginijus, Sviklas, Alfredas Martynas, Baltrusaitis, Jonas
ACS sustainable chemistry & engineering 2018 v.6 no.7 pp. 9427-9433
NPK fertilizers, drums (equipment), electrochemistry, environmental impact, feedstocks, greenhouse gas emissions, greenhouse gases, land use, magnesium, manufacturing, mining, porous media, potassium, potassium chloride, processing waste, sludge, solid wastes, surface area, sustainable engineering, trace elements
Principles of green engineering require that material inputs are renewable. To this regard, a partial or a full substitution of one of the feedstocks with the waste from other industries can minimize the environmental impacts. Potash rock is a source of a key potassium (K), but its environmental impacts, including land use and greenhouse gas emissions during the mining and beneficiations, are of concern. Carnallite rock is used to electrochemically produce elemental magnesium (Mg) and yields solid sludge waste with K₂O content of ∼43% and Mg content of 2.0%.This carnallite-derived waste is characterized physically and chemically and utilized to manufacture compound NPK fertilizers. The mesoporous waste material structure was found which facilitated the wet granulation process in spite of low 6 m²/g measured surface area. Trace metal concentrations measured were low and did not pose significant limitations from the regulatory point of view. Several high-K₂O-content fertilizer formulations were proposed and granulated using both laboratory and industrial wet granulation in a rotary drum. Large K₂O amount from the carnallite processing waste, up to 10 times that from mined KCl, was utilized in these fertilizers. The sustainability impact of the overall process was assessed by evaluating the averted greenhouse gas (GHG) emissions when carnallite-derived waste was substituted for potash rock. It was found that up to 5000 t of CO₂/year per 100 000 t/year NPK 10-20-20 fertilizer can be avoided if waste is used rather than the potash rock.