NEW ROLES OF COBALT FOR ENHANCED CRITICAL MINERAL SEPARATION AND EXPANDING NATURAL CEMENT STABILITY

Separation and reprocessing of critical minerals from bulk materials like ore, rock, and waste is necessary to obtain these vital materials and keep them in an available form for use. Although elemental cobalt is sought as a crucial element driving several industries, its versatility as a coordination complex has many uses in research and industrial processes. I present here work performed using the hexanitritocobaltate (III) ion as a mechanism for enhanced separation of the critical mineral magnesium from complex geological samples. This complex ion may also have utility in isolating detrimental alkalis in cement and concrete, particularly in the Pennsylvania Geological Survey’s search for suitable replacements for historically used, lower-emissions, “natural cement” created from suitable impure dolomites.

Magnesium (Mg) is a critical mineral that is both a major rock-forming element and expensive to isolate as the base metal. Separation of Mg and other cations from geological samples can be performed through cation-exchange sulfonic acid resins (e.g., BioRad AG50), though methods are time- and labor-intensive due to overlaps in elution peaks. Through addition of sodium cobaltinitrite (sodium hexanitritocobaltate (III), Na₃[Co(NO₂)₆]) and ethanol, quantitative extraction of potassium can be achieved through precipitation of an insoluble, mixed potassium-sodium cobaltinitrite (K₂Na[Co(NO₂)₆]). As there can be significant elution overlap between K and Mg, removal of K greatly reduces processing time. The cobaltinitrite ion can be decomposed through acid treatment, liberating the cobalt for reuse.

A major barrier in our search for suitable impure dolomites for “natural cement” is the minimization of alkalis in the source rocks due to their destructive effects in a cement product. One otherwise excellent target for natural cement production we are exploring contains authigenic microcline. Although mechanical separation may be able to remove most of this microcline before sintering, addition of calcium nitrite (already used as a corrosion inhibitor for steel embedded in concrete) and cobalt nitrate after sintering could bind and sequester residual K as the insoluble potassium cobaltinitrite within the portlandite pore solutions in concrete.