L.R.P. de Andrade Lima

Characterization of the lead smelter slag in Santo Amaro, Bahia, Brazil

For 33 years, a primary lead smelter operated in Santo Amaro (Brazil). Since the 1970s, large amounts of Pb and Cd have been widely documented in the blood and hair of people living near the smelter. The plant closed down in 1993, and several years later, the Pb levels in the blood of children under 4 years of age living near the smelter were high, where the disposed lead slag was suspected to be the main source of this contamination. The objective of this study is to elucidate the source of the Pb contamination and any other potentially toxic contamination, focusing on the characterization of the slag. The samples used for this characterization study were taken from the slag heaps. The results of the chemical analysis showed that the major constituents of the slag, in decreasing order of wt%, were the following: Fe(2)O(3) (28.10), CaO (23.11), SiO(2) (21.39), ZnO (9.47), MgO (5.44), PbO (4.06), Al(2)O(3) (3.56), C (2.26), MnO (1.44), Na(2)O (0.27), S (0.37), K(2)O (0.26), and TiO(2) (0.25). The Cd content of the slag was 57.3mg/kg, which is relatively low. The X-ray diffraction and the electron probe microanalyzer X-ray mapping indicated that the major phases in the slag were wüstite, olivine, kirschsteinite, and franklinite. Only spheroidal metallic Pb was found in the slag. The leaching study showed that the slag was stable at a pH greater than 2.8, and only in an extremely acidic environment was the solubilization of the Pb enhanced significantly. The solubilization of Zn was very limited in the acidic and alkaline environments. These results can be explained by the limited leachability of the metallic Pb and Zn-bearing compounds. The leaching study used TCLP, SPLP, and SWEP and indicated that the lead slag was stable in weak acidic environments for short contact times.

Poiseuille flow of Leslie–Ericksen discotic liquid crystals: solution multiplicity, multistability, and non-Newtonian rheology

Abstract Computational modeling of the steady capillary Poiseuille flow of flow-aligning discotic nematic liquid crystals (DNLCs) using the Leslie–Ericksen (LE) equations predicts solution multiplicity and multistability. The phenomena are independent of boundary conditions. The steady state solutions are classified into: (a) primary, (b) secondary, and (c) hybrid. Primary solutions exist for all orientation boundary conditions and all flow rates, and are characterized by a flow-alignment angle that is closest to the anchoring angle at the bounding surface. Secondary solutions exist for all orientation boundary conditions and flow rates above a certain critical value. The secondary solutions are characterized by a flow-alignment angle which can be either the nearest neighbor below the primary solution or any multiple of π above. Hybrid solutions interpolate between the primary and the nearest secondary solutions, and hence exhibit two alignment angles. All solutions are stable to planar finite amplitude perturbations. Hybrid solutions are unstable to front propagation and lead to primary or secondary solutions. The non-Newtonian rheology of the primary and secondary solutions is characterized by non-classical shear thinning and thickening apparent viscosity behavior. Well-aligned monodomains can lead to shear thickening, thinning, or a sequence of both. The degree of rheological uncertainty is present for planar and homeotropic anchoring conditions. The non-Newtonian rheology of non-aligned samples leads to shear thinning and lack the uncertainty of well-aligned samples, since the apparent viscosity becomes insensitive to orientation.

A mathematical model for isothermal heap and column leaching

Leaching occurs in metals recovery, in contaminated soil washing, and in many natural processes, such as fertilizer dissolution and rock weathering. This paper presents a model developed to simulate the transient evolution of the dissolved chemical species in the heap and column isothermal leaching processes. In this model, the solid bed is numerically divided into plane layers; the recovery of the chemical species, the enrichment of the pregnant leach solution, and the residual concentration of the leaching agent are calculated by interactions among the layers. The solution flow in the solid bed is assumed as unidirectional without dispersion, and the solid-fluid reaction is described by a diffusive control model that is integrated analytically for each time step. The data set used in the model include physical-chemical, geometrical, and operational variables, such as: leachable chemical species content, leaching agent flow rate and concentration, particles size distribution, solution residence time in the solid bed, and solid bed length, weight and irrigated area. The results for two case studies, namely, an industrial gold heap leaching and a pilot column copper acid leaching, showed that the model successful predict the general features of the process time evolution.

Superposition and universality in the linear viscoelasticity of Leslie-Ericksen liquid crystals

The linear viscoleasticity of seven lyotropic and thermotropic liquid crystalline polymers is characterized using the Leslie–Ericksen equations of defect-free nematodynamics for small amplitude oscillatory capillary Poiseuille flow, using analytical, numerical, and scaling methods. The experimentally measured seven data sets correspond to shear flow-aligning and shear nonaligning materials. The predicted equivalent rheological responses between these two classes of polymers demonstrate the universality of nematodynamics. Principles of superposition are developed, applied, and shown to be accurate in collapsing the data sets for aligning and non-aligning polymers. The scaled resonance peak in the loss tangent (G″/G′) is shown to be a universal constant for monodomain nematics.

Linear and nonlinear viscoelasticity of discotic nematics under transient Poiseuille flows

The start-up, reversal, and cessation of capillary Poiseuille flows of uniaxial isothermal incompressible discotic nematic liquid crystals are characterized using analytical, computational, and scaling methods, for low (linear regime) and high (nonlinear regime) pressure drops. In the linear regime, transient flows provide information on the main viscoelastic material properties, including the steady shear Miesowicz’ viscosity, the transient reorientation viscosity, as well as the viscosity reduction due to backflow. It is shown that cessation of weak flow provides a way to measure pressure drops. Transient flows in the nonlinear regime involve orientation-dependent material functions. The flow rate in start-up is characterized by an overshoot and strain scaling, similar to stress overshoot in simple shear. Recoil after cessation of flow is shown to be a direct function of stored Frank elastic energy. Scaling and computation show that the maximum recoil volume is shown to be close to R3, where R is the ca...

Dynamic simulation of the carbon-in-pulp and carbon-in-leach processes

Carbon-in-leach and carbon-in-pulp are continuous processes that use activated carbon in a cascade of large agitated tanks, which have been widely used to recover or concentrate precious metals in gold extraction plants. In the carbon-in-pulp process adsorption occurs after the leaching cascade section of the plant, and in the carbon-in-leach process leaching and adsorption occur simultaneously. In both processes the activated carbon is moved from one tank to another in countercurrent with the ore pulp until the recovery of the loaded carbon in the first tank. This paper presents a dynamic model that describes, with minor changes, the carbon-in-leach, the carbon-in-pulp, and the gold leaching processes. The model is numerically solved and calibrated with experimental data from a plant and used to perform a study of the effect of the activated carbon transfer strategy on the performance of the adsorption section of the plant. Based on the calculated values of the gold loss in the liquid and of the gold recovered in the loaded activated carbon that leaves the circuit, the results indicate that strategies in which a significant amount of activated carbon is held in the first tank and the contact time between the carbon and the pulp is longer are the best carbon transfer strategies for these processes.

Multiscale simulation of flow-induced texture formation in polymer liquid crystals and carbonaceous mesophases

This paper presents theory and simulation of flow-induced structures in liquid crystalline materials, useful to the creation of synthetic material structures and to the biomimetics of natural fibers. A multiscale theory and simulation of hydrodynamic texture formation is presented; it provides fundamental principles for control and optimization of structures in liquid crystal polymers and carbonaceous mesophases. In thermotropic flow-aligning nematic polymers it is found that as the shear-rate increases, the pathway between an oriented non-planar state and an oriented planar state is through meso-texture formation and coarsening, with temperature and shear rate being efficient fields to control the grain size of the texture. For capillary flow of carbonaceous mesophases, the simulations predict the emergence of macroscopic ring patterns whose thickness and density can be controlled by the applied pressure drops. The results provide insight on microstructure formation and control in liquid crystalline materials.

Isotope Source Signatures for a Primary Lead Smelter Located Close to Todos os Santos Bay, Brazil

From 1960 to 1993, a primary lead smelter operated in the Santo Amaro region, close to Todos os Santos Bay in Brazil, using the classical sinter-roasting process followed by smelting and refining. A high lead content was found in the sediments from Todos os Santos Bay, which has a large circulation and receives the discharge from three rivers. Lead stable isotope ratios provide information about the ore mineralization and can be used to evaluate the origin and fate of the lead pollution. The objective of this study is to identify the isotopic signature of the major effluents of this lead smelter and correlate it with the origin of the galena concentrate that generated it. The X-ray microanalysis confirms that the lead occurs in the slag in the metallic state. The soil has a high lead content (about 0.90%) of oxidized lead. The lead isotopic ratios indicated that the slag isotopic ratios (208Pb/204Pb = 34.8; 207Pb/204Pb = 15.3; 206Pb/204Pb = 15.1) are close to the soil value (208Pb/204Pb = 36.2; 207Pb/204Pb = 15.9; 206Pb/204Pb = 16.4) and both agree with the values for the galena from the Boquira mine region (208Pb/204Pb = 34.6±1.1; 207Pb/204Pb = 15.3±0.4; 206Pb/204Pb = 14.7±0.2). These results indicate that no isotopic fractionation occurred in the roasting-smelting process, therefore the original Boquira isotope ratios can be used as the isotopic signature of the lead dispersed from the Santo Amaro smelter.

Improved method for enumerating sulfate-reducing bacteria using optical density

Graphical abstract

Back‐flow and flow‐alignment in pulsatile flows of Leslie–Ericksen liquid crystals

Analytical solutions to the capillary pulsatile flow of Leslie–Ericksen liquid crystals under small pressure drops are presented, when the imposed small pressure drop contains a steady and a time‐periodic contribution. The results show that pulsatile flows initiate periodic back‐flows (reorientation‐induced flow) which are directly linked to flow‐alignment characteristics of the material. The experimentally measurable power requirement (flow rate×pressure drop) is shown to be well suited to quantify back‐flows and flow‐alignment material properties. The analysis reveals that power requirements deviate from the Newtonian limit when the frequency of the oscillating pressure drop is close to the splay orientation diffusivity, and backflows become significant. In the terminal zone (small frequencies) the response is Newtonian and the power requirement is a quadratic function of amplitude. At large frequencies, the amplitude of back‐flow effects saturates and the power requirement is proportional to the square of the alignment viscosity coefficient α3. An experimental procedure to measure the flow‐alignment viscosity coefficient α3 is formulated, based on large frequency measurements, and a formula derived from the close‐form solution to the Leslie–Ericksen equations for capillary pulsatile flows.