The thermal safety of chemical processes requires knowledge of the safety parameters that quantify the probability, such as time to maximum rate under adiabatic conditions (TMR ad ), and the severity, such as adiabatic temperature rise under adiabatic conditions (ΔT ad ). The zero-order approximation is used to ease the determination of TMR ad values at different process temperatures; but how can one be sure that this approximation is acceptable, compared to the use of an intrinsic kinetic model? In the literature, there are no such studies that compare the values of TMR ad by using zero-order and intrinsic kinetic models. For that, decomposition of hydrogen peroxide in the presence (and in the absence) of copper sulfate was studied in an advanced reactive system screening tool (ARSST) unit. This calorimeter operates under near-adiabatic conditions, based on heat loss compensation principle, and by using a background heating rate (β). In a first stage, a kinetic model was built to estimate the intrinsic kinetic constants. Then, a comparison between the values of TMR ad from the zero-order and the intrinsic kinetic model was performed. It was found that the difference of TMR ad values obtained by these two models can be significant. The influence of β and reactant concentrations were found to play an important role in this difference. As good practice, in the case of missing kinetic and thermodynamic data, a user should test different background heating rates to verify their influence on TMR ad values obtained from the zero-order model.
We report the investigation
of a chalcopyrite leaching process
that implements millimeter-sized glass beads that are stirred in the
leach reactor to combine particle grinding, mechanical activation,
and surface removal of reaction products. The paper focuses on demonstrating
the impact of the so-called attrition-leaching phenomenon on the leaching
rate of a chalcopyrite concentrate and provides a first understanding
of the underlying mechanisms. For this purpose, we have compared the
copper leaching yield for different configurations under controlled
chemical conditions (1 kg of glass beads and 84 g of chalcopyrite
concentrate in 2.5 L of H2SO4-H2O
solution, pH = 1.3, E
h = 700 mV vs SHE,
and T = 42 °C). On top of elemental analysis
of the leach solution with time, we provide a full characterization
of the solid residue based on X-ray diffraction, elemental analysis,
and sulfur speciation. We demonstrate that glass beads led to a remarkable
enhancement of the leaching rate in conditions where particles were
already passivated by simple leaching and even when large amounts
of solid products (elemental sulfur and jarosite) were present. An
in-depth evaluation of particle size distribution showed that particle
breakage occurred during a rather short time (a few hours) at the
beginning of the runs, transforming the initial particles with d
4/3 = 30 μm to finer particles with d
4/3 = 15 μm. Then, particle breakage almost
stopped, while an attrition phenomenon was evidenced, inducing the
formation of very fine particles (<1 μm) and aggregates concomitantly
with copper leaching.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.