Potentiality of caro’s acid in leaching of uranium and radioactive measurements from Abu-Rusheid mylonitic gneiss rocks, South Eastern Desert, Egypt

Abu Rusheid area is located at the Southern Eastern Desert of Egypt and composed of Mylonitic gneiss rocks (mineralized rock), Serpentinite rocks, Ophiolitic metagabbro, Ophiolitic mélange, Monzogranites, post- granitic dykes (lamprophyre and dolerite), veins and recent alluvial deposits. This paper is concerned with the study of potentiality of sulphuric and caro’s acid in uranium dissolution from Abu Rusheid mineralized rocks. For this purpose, many batch dissolution experiments were conducted. The obtained results showed that 91.5% and 52% uranium leachability for Caro’s acid and dilute sulfuric acid respectively. The reaction mechanism was described using shrinking core models.

Do oscillating redox conditions affect long-term Si release from phytoliths?

<p>Phytoliths are a major source of plant-available Si in weathered soils, particularly for crops with high Si demand, such as rice. Yet, not much is known about the evolution of Si release from phytoliths under real soil conditions. The extraction of phytoliths from soil is difficult and usually leads to changes in phytolith surface chemistry. Paddy rice cultivation induces oscillations in redox potential by alternating submergence and drainage. These oscillations may have a major impact on the evolution of phytolith Si release. For instance, reduced Fe<sup>2+</sup>, abundantly in solution under low redox potential may sorb onto negatively charged phytolith surfaces and form iron oxide coatings when redox potential rises after drainage. We thus hypothesise that phytolith Si release decreases with time in soil as phytolith surfaces are increasingly coated with oxides and organic matter. To test the effect of oscillating redox potential on phytolith surface chemistry and implicit changes in Si release we conduct experiments with phytoliths extracted from rice straw by dry ashing. Extracted phytoliths are sequentially exposed to soil solutions with contrasting redox potentials (anoxic vs. oxic), using either alternating anoxic-oxic solutions or exclusively oxic solutions. Anoxic exposure is conducted in Ar atmosphere (< 1% O<sub>2</sub> partial pressure). After each exposure events the filtrate is analysed for pH and redox potential, Fe<sup>2+</sup> with the Ferrozine method, and total Fe, Al and Si with inductive-coupled plasma-optical emission spectrometry. Filter residues are sampled and analysed after 1, 2, 4, and 8 exposure steps (each lasting 2 hours), respectively. Surface chemical composition is analysed with X-ray photoelectron spectroscopy. Specific surface area is determined with N<sub>2</sub> gas adsorption at 77 K and surface charge is measured by determining electrophoretic mobility using dynamic light scattering. Batch dissolution experiments in mini-reactors are carried out for assessing the Si release of untreated and treated phytoliths. The experimental results will provide important information on the changes of phytolith surface chemistry and Si release from phytoliths in systems with alternating redox potentials such as rice paddies.</p>

Dependence of Stability of Sr5(AsO4)3OH on pH Value

The object of this work was to determine the solubility and stability of the synthetic Sr5(AsO4)3OH solid solution at 25°C and the different initial pHs (pH at 2, 6 and 9) by batch dissolution experiments. The results indicated that with the initial pH value of 2, 6 and 9, the reaction system reached equilibrium after 2880h, and by that time the pH value of the solution reached, 7.90, 8.74 and 8.27 respectively. The concentration of strontium and arsenic in the initial solution pH at 2 are higher than that of solutions pH at 6 and 9. While the concentration of strontium in neutral or alkaline solutions is low and stays unchanged.

Lead Immobilization and Hydroxamate Ligand Promoted Chloropyromorphite Dissolution

The immobilization of lead, a major environmental contaminant, through phosphate amendments to form the sparingly soluble lead phosphate mineral chloropyromorphite [Pb5(PO4)3] (CPY) is an effective in situ strategy for soil remediation. An important question is the effect of microbial processes on this remediation. Here, we investigate the role of the microbial siderophore ligand desferrioxamine-D1 (DFO-D1) and its analog acetohydroxamic acid (aHA) in CPY lability using pH-dependent batch dissolution kinetics and model calculations. Both (0.01) M aHA and (0.00024) M DFO-D1 are similarly effective and enhance lead release from CPY by more than two orders of magnitude at pH > 6 compared to in the absence of ligands. This is consistent with model calculations of pH-dependent (aqueous) complexation of lead with hydroxamate ligands. More importantly, pH-dependent ligand sorption is predictive of its ligand promoted dissolution behavior. Our results suggest that organic ligands can significantly increase CPY lability at alkaline pHs in soils and sediments and that addition of P amendments to immobilize Pb as CPY may only be successful at acid pHs.

The Characteristic Dissolution and Physical Chemistry Parameter of Synthetic Pyromorphite

The Dissolution of Synthetic Pyromorphite was Studied at 25°C in a Series of Batch Experiments. in Addition, the Aqueous Concentrations from the Batch Dissolution were Used to Calculate the Solubility Product and Free Energy of Formation of Pyromorphite. the Results of the Fourier Transform Infrared Spectroscopy Analyses Indicated that the Synthetic, Microcrystalline Pyromorphite with Apatite Structure Used in the Experiments has Not Changed after Dissolution. the Mean KspValue was Calculated for Pb5(PO4)3Cl of 10-78.31 at 25°C; the Free Energy of Formation ΔGf0[Pb5(PO4)3Cl] was-3756.82kJ/mol.

Association of trace elements and dissolution rates of soil iron oxides

In this study, nine Oxisols and five Ultisols from Thailand were used to determine the association of major and trace elements with iron (Fe) oxides. The Fe oxides were concentrated and the association of elements (Al, Ca, Cu, Cr, Mg, Mn, Ni, Pb, P, Si, V, Ti, Zn) with Fe was evaluated using batch dissolution in 1 m HCl at 20°C. The dissolution behaviour of Fe oxide concentrates was determined using batch dissolution and flow-through reactors. In addition to Fe, both Al and Ti were present in significant amounts in the Fe oxide concentrates. Manganese was the most abundant trace element, and Cu, Zn, Pb and As concentrations were <250 mg kg–1 in most samples. The dissolution behaviour of Fe-oxide concentrates indicated that Al, Cr and V were mostly substituted for Fe3+ in the structure of goethite and hematite. A significant proportion of Mn, Ni, Co, Pb and Si was also present within the structure of these minerals. Some Mg, Cu, Zn, Ti and Ca was also associated with Fe oxides. The dissolution kinetics of Fe oxide concentrates was well described by three models, i.e. the cube root law, Avrami–Erofejev equation and Kabai equation, with the dissolution rate constants (103k) corresponding to the three models ranging from 0.44 to 6.11 h–1, from 1.01 to 4.40 h–1 and from 0.03 to 4.12 h–1, respectively. The k constants of Fe oxide concentrates in this study were significantly and negatively correlated with the mean crystal dimension derived from [110] and [104] of hematite, the dominant mineral in most samples. The steady-state dissolution rate of a soil Fe-oxide concentrate (sample Kk) was substantially higher than for synthetic goethite under highly acidic conditions; this is possibly due to the greater specific surface area of sample Kk than the synthetic goethite.

Characterization, Dissolution and Solubility of Pyromorphite [Pb5(PO4)3Cl] at 25°C

Pyromorphite was synthesized by precipitation and characterized by various techniques. The batch dissolution experiment was conducted at 25°C and different initial pHs (2, 4 and 6). The solid phase showed no obvious change before and after dissolution. The aqueous phosphate concentration decreased quickly from 0.22 to 0.01mmol/L and then increased very slowly with time. After 2160h dissolution, it reached a steady-state value of about 0.13mmol/L. The aqueous lead concentration increased initially and reached a peak value after 72h dissolution.