Sanchez-Pastor, Nuria; Kaliwoda, Melanie; Veintemillas-Verdaguer, Sabino; Jordan, Guntram
On the effect of carbonate on barite growth at elevated temperatures.
In: American Mineralogist, Vol. 98, No. 7: pp. 1235-1240
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The effect of carbonate on the growth of barite 50016 surfaces fromaqueous solutions supersaturated with respect to barite (Omega(barite)similar to 12) was studied by hydrothermal atomic force microscopy (HAFM) and Raman spectroscopy at temperatures ranging from 25 to 70 degreesC. The experiments showed that the effects of carbonate depend on thespecific location of growth. For mono-layers growing on pristine barite,the carbonate-additive promotes growth and the spreading rate oftwo-dimensional islands increases with temperature. However, growth isinhibited in layers growing on surfaces, which grew incarbonate-containing solution. The threshold carbonate concentrationnecessary to completely inhibit growth is inversely correlated withtemperature. Raman spectroscopy revealed the presence of carbonatewithin crystals, which grew in carbonate-containing solution. Judging bythese findings, incorporation of carbonate into the structure of growingbarite as a thermally activated process likely is a controlling factor,which inhibits barite growth. Thus the study shows that additives canexert opposing effects on growth not only depending on additiveconcentration but also depending on the specific growth location. Theimplication of this work, therefore, is that bimodal effects ofadditives on crystal growth occur more frequently than generallyrecognized. The insights into the mechanisms of such bimodal effects ofadditives can significantly contribute to the understanding andpredictability of the kinetics of macro-scale processes such as baritescale formation or the behavior of barium sulfate in CO2-sequestrationfluids.