RESUMEN
This report describes the characterization of a sedimentary occurrence from the Parnaíba Basin, Brazil, containing the zeolite stilbite intertwined with smectitic clay mineral. The head samples from different sites present a wide content range of the zeolitic phase - 15 percent to 50 percent. The use of simple separation techniques - conventional gravitic treatments - yields concentrates containing about 67 percent of the zeolitic component. Assays with the amendments of these concentrates with plant nutrients yield release rates matching those reported for similar commercial products.
São apresentadas as propriedades físico-químicas de uma ocorrência sedimentar da Bacia do Parnaíba, Brasil, da zeólita estilbita, agregada a uma argila esmectítica. As amostras de diferentes sítios apresentam uma ampla variação do mineral zeolítico: entre 15 por cento a 50 por cento. A utilização de espirais concentradoras foi suficiente para obtenção de concentrados contendo até 67 por cento do mineral. Ensaios laboratoriais do concentrado dopado com fertilizantes revelam taxas de liberação de nutrientes comparáveis aos obtidos com produtos comerciais similares.
RESUMEN
The present study is based on the proposal that if the aqueous phosphorus-capture mechanism by iron oxide precursors was inhibited in prebiotic anoxic scenarios then soluble phosphates could have been more available than what is observed now. Supporting this conjecture, we examine prevailing contemporary trapping mechanisms of orthophosphate (Pi) and pyrophosphate (PPi). To illustrate its efficiency, the attachment of (Pi) onto aggregates of iron-3 oxyhydroxide is compared with the one reported for the product of its condensation, PPi. The electrophoretic profiles of the Pi- and PPi-aggregate complexes reveal different pH-modulated interactions of the phosphorylated compounds with both the aggregate and its aqueous surrounding layers. The observed differences of Pi/PPi sorption and desorption mechanisms are discussed in terms of their consequences to the prebiotic availability of soluble orthophosphate and of a phosphorylated compound having the high-energy phosphoanhydride linkage and a molecule representative of condensed oligophosphates.