Leaching Duration Research Articles

The relationship between fluid flow and mineral weathering in heterogeneous unsaturated porous media: A physical and geochemical characterization of a waste-rock pile

The relationships between factors that control subsurface flow and the timing, duration, and intensity of acidity generation and leaching of metals from waste-rock dumps are investigated. A 12 m high waste-rock pile that had been constructed in 1994 at Key Lake, Saskatchewan, Canada was disassembled, sampled and characterized in 2000. Physical properties that control water flow were characterized by measuring soil–water suction, volumetric water content, and the grain-size distribution at 60 randomized sites within the pile. Grain-size distribution was also measured at an additional 20 grid locations within the pile. Paste pH, pore-water geochemistry, mineralogy, and water-soluble extractions were used to investigate geochemical processes and sulfide oxidation at each of the 20 grid locations. A field-based soil–water characteristic curve could not be developed from the spatially variable and hysteretic field data; consequently, the grain-size distribution was used as a relative measure of subsurface flow and of the tendency to contain water under unsaturated conditions. The geochemical characterization demonstrated that marcasite underwent preferential weathering relative to pyrite and chalcopyrite, that dolomite was the main buffering carbonate mineral, and that gypsum, jarosite, and Fe oxyhydroxides were the main secondary (supergene) minerals. The pore waters contained up to 78,000 mg L −1 SO 4, 690 mg L −1 Ni and 1400 mg L −1 U (800, 11.7 and 6 mM, respectively), suggesting that significant weathering had occurred. The pore water chemistry varied considerably between sampling sites. However, neither a correlation of pore-water chemistry with grain-size distribution nor a spatial relationship within the sampled grid was discernible.

Modelling of bituminized radioactive waste leaching. Part II: Experimental validation

This paper presents experimental work aiming at studying the behaviour of leached bituminized waste materials and the development of a saline solution-filled pore structure (called permeable layer) in the materials. Standard leach tests are performed on two synthetic BW materials containing different soluble salt contents and leached by solutions of varying chemical activities. The water uptake and the sodium nitrate leach rates are measured continuously during the tests. Porosity profiles are obtained from ESEM image analyses performed on the same BW samples leached during periods of varying durations. These experimental results provide a precise description of the internal structure of BW materials during leaching. The impact of the leaching duration, of the soluble salt content, and of the chemical activity of water in the leachant on the overall behaviour of leached BW materials is by this way assessed and compared to the theoretical trends presented in Part I of this paper.

The Leaching Behavior of Cadmium, Arsenic, Zinc, and Chlorine in Coal and Its Ash from Coal-Fired Power Plant

The leaching experiment of feed coal (C) and its laboratory high-temperature ash (HA), fly ash (FA), and bottom ash (BA) from a Chinese coal-fired power plant were carried out using column leaching under different pH conditions (pH = 2.0, 4.0, 6.0, and 7.5, respectively) and different leaching durations (up to 80 h). The leaching behaviors of As, Cd, Zn, and Cl were investigated. The results showed that the elements occurring in water-soluble, ion-exchangeable, and Fe–Mn oxide phases are potentially leachable, whereas those in association with organic matter and silicate are less likely to be leached. The cumulative percent of Zn, As, Cl, and Cd leached from C and ash samples increase with decrease in pH. The leaching rate of As and Cl in C and ash samples are higher in comparison with Zn and Cd. However, the maximum concentrations of Cd in the leachate from C, HA, FA, and BA are in excess of or very close to the maximum standard concentrations permitted in the Chinese Standards for Drinking Water and Surface Water. The ultimate concentrations of As, Cd, and Cl in the leachates did not attain equilibrium after the leaching of 80 h; therefore, longer leaching experiments are necessary to evaluate the impact of these hazardous trace elements on aqueous environment.

U environment in leached SON68 type glass: a coupled XPS and time-resolved photoluminescence spectroscopy study

X-ray photoelectron spectroscopy (XPS) and time-resolved photoluminescence measurements have been performed on SON68 type nuclear glass and its leached product (gel) in order to characterize uranium environment in both materials. XPS measurements allow to detect two oxidation states in glass: about 20% of tetravalent uranium and 80% of hexavalent uranium, present under two types of environment. Comparison of XPS and time-resolved photoluminescence data allow to identify these U(VI) environments. In glass, they are respectively attributed to an uranate and an uranyl-type environment. In gels, U(IV) is oxidized in U(VI), the uranyl type environment is conserved whereas some amorphous uranyl hydroxides are formed. The U environment depends strongly on the leaching mode, in particular the leaching duration and water renewal rate.

Aqueous SO 2 leaching studies on Nishikhal manganese ore through factorial experiment

Aqueous SO 2 leaching studies of Nishikhal manganese ore containing 32.5% Mn and 16.5% Fe were carried out at atmospheric pressure and room temperature using H 2SO 3. The variables considered were SO 2 concentration, solid-to-liquid ratio, sulphuric acid concentration and duration of leaching. Regression equations for extraction of manganese and iron were determined from 2 4 full factorial design. The effect of variables on extraction of manganese were independent of each other within the range of variables chosen for experiment. It was found that 95% of manganese could be extracted in 15 min from −150 μm ore with twice the stoichiometric quantity of SO 2 required for dissolution of manganese. The quantity of SO 2 present in the solution is the controlling factor in the extraction of manganese.

In-Vitro Determination of Arsenic Bioavailability in Contaminated Soil and Mineral Beneficiation Waste from Ron Phibun, Southern Thailand: A Basis for Improved Human Risk Assessment

The post-ingestion bioavailability of arsenic (As) in alluvial soil and mineral beneficiation waste from Ron Phibun, Nakhon Si Thammarat Province, Thailand has been investigated using a physiologically-based extraction test (PBET). The method utilises synthetic leaching fluids closely analogous to those of the human stomach and small intestine, upon which the leaching duration and ambient temperature of the experimental procedure are also directly based. Replicate analyses of Ron Phibun alluvium samples holding 1406 and 2123 μg As g-1 respectively indicated an average stomach absorption of 11.2% (of total soil As). Gross absorption increased to 18.9% following translocation through a simulated small-intenstine regime. Higher gross absorption (35.7%) was recorded during PBET analysis of a flotation waste sample holding c. 2% total As. Within- and between-site variations of As bioavailability can principally be ascribed to mineralogical factors, notably the relative abundances of sulphide, arsenide, arsenate and oxide hosts within the soil/flotation waste matrix. The PBET provides a potentially valuable mechanism for refining risk assessments of sites subject to natural or anthropogenic As contamination. Through the substitution of total soil As values with input data which relate specifically to bioavailable As, risk calculations derived using established models such as the US-EPA package Risk Assistant may prove more realistic, thus facilitating improved cost-benefit analysis of site remediation options. Assessment of the relative human risks associated with potable water consumption and contaminated soil ingestion at Ron Phibun has signified that the latter could constitute a more significant As exposure pathway than recognised previously. Further evaluation of the precise soil ingestion levels of inhabitants residing on the As-rich alluvium which covers much of the district is, therefore, warranted.

Thiourea leaching of a copper-gold ore using statistical design

Thiourea was used to leach gold from ore containing 0.4% Cu and 5.6 g/t Au. The parameters studied were acid pretreatment, leaching time, pH, thiourea concentration and the oxidizing agents used. Gold extraction was 89% and thiourea consumption was 3.9 kg/t. No acid consumption was observed during leaching at pH 3. Pretreatment by acid washing is recommended for improved gold leaching and lower thiourea consumption. The best gold recovery results were obtained with ferric sulphate as the oxidizing agent, although it is more expensive. Thiourea dissolves three times less copper than cyanide does. The best leaching conditions achieved were as follows: acid wash pretreatment, an average amount of added thiourea of 12 g/, a leaching duration of 72 h and a pH of 3. The oxidation-reduction potential fluctuated between 410 and 450 mV/SHE.

Impact des produits de lessivage de feuilles mortes sur la teneur en oxygène de l'eau et sur la survie d'un gastéropode

The impact of the leaching of oleander, Nerium oleander, and willow, Salix pedicellata, leaves on the aquatic environment was investigated in the laboratory. The leaves were collected on the banks of a Moroccan stream, leachate polyphenols were analysed, and leachate toxic effects on the dominant gastropod species of the stream were investigated. The following factors were considered: leaf species, dry or fresh state of the leaves, litter concentration, duration of leaching, temperature. o 1) Within the first 8–12 hrs of submersion, the litter of both species caused a great depletion of dissolved oxygen. Later, oxygen consumption decreased. Dry oleander leaves caused a greater drop in oxygen concentration than fresh oleander leaves. The opposite was observed in willow leaves, most clearly at 5 and 10°C. At higher temperatures (20 and 25°C), oxygen nearly totally disappeared under all conditions, leaving 0 to 2 mg.I −1 after 48 hours. Whether fresh or dry, oleander leaves always caused a greater oxygen depletion than willow leaves. 2) Willow leaves contained more tannin-and non-tannin-polyphenols than oleander leaves, and their leaching released more of these compounds, especially in dry leaves. 3) The leaching of both leaf species only had a toxic effect on the gastropods at the higher temperatures (20 and 25°C), thus suggesting that the toxic effect was mainly due to lack of oxygen in the water. At these temperatures, the toxic effect of dry leaves was greater than that of fresh leaves. Oleander proved more toxic than willow, presumably under the influence of both lack of oxygen and toxic heterosides.

Leaching of Nitrogen from Slow‐Release Urea Sources in Sandy Soils

AbstractApplication of readily soluble forms of N fertilizers to sandy soils may cause leaching of NO3‐N resulting in contamination of groundwater. The leaching loss of N may be reduced to some extent by using slow‐release forms of N. An intermittent leaching and incubation technique, to mimic natural occurrence of rainfall and dry conditions, was used to examine the leaching of N from readily soluble (NH4NO3) and slow‐release fertilizers [isobutylidene diurea (IBDU) and a polyolefin resin‐coated urea, Meister] in Wabasso (sandy, siliceous, hyperthermic Alfic Haplaquod) and Candler (hyperthermic, uncoated Typic Quartzipsamment) soils. After 29 d, the cumulative recovery of the applied fertilizer N in the leachate for the treatments decreased in the following order: NH4NO3 (88‐100%) > IBDU (27–32%) > Meister (11.5–11.7%). A significant portion (19.5–35.5%) of the total N leached from IBDU and Meister was in the urea form in the initial leaching; however, after 9 d, NO3 and NH4 forms represented the major portion of leachate total N. Although N from NH4NO3 was leached completely from the Candler sand, 12% of the applied N (as NH4NO3) was not recovered in the leachate from the Wabasso sand. Cumulative NH4‐N leached from the Wabasso sand was only 58% of that from the Candler sand. The results demonstrate that the amounts and forms of fertilizer N leached from the sandy soils depend on the solubility of the fertilizer, the soil type, and the duration of intermittent leaching.

Leaching of hydrogen peroxide from bleached bovine enamel

Accurately weighed bovine enamel slabs were individually immersed in 2 ml of 35% hydrogen peroxide for 1, 3, 5, 30, or 60 min. A control group was obtained by individual immersion of bovine enamel slabs in 2 ml of saline for 60 min. All samples were washed, dried, acid-etched with 37% phosphoric acid for 60 s, then washed and dried again. Two milliliters of double-distilled water were used for individual sample leaching. Leaching was done for 1, 5, 10, 20 min, or 7 days for the experimental groups and for 7 days for the control group. The samples of one of the experimental groups were leached for a second time for 1 min. A total of 112 samples was used in this study. Hydrogen peroxide was spectrophotometrically identified and quantified in all leaching solutions based on the oxidation reaction of leuco-crystal violet buffer solution by hydrogen peroxide, a reaction catalyzed by horseradish peroxidase. The results revealed a significant difference in the quantity of leached peroxide between bleached samples (irrespective of the duration of leaching) and control, saline-treated ones. No difference was observed in the quantity of leached peroxide between releached samples and control, saline-treated ones. However, these were small, random, and numerically insignificant. Statistically significant differences were also noted among some of the experimental groups. They were thought to hold no clinical significance. The results suggested that upon immersion, the complete leaching of peroxide from bleached enamel occurs rapidly.

Leaching of copper converter slag withAspergillus niger culture filtrate

Leaching of copper converter slag of M/s Hindustan Copper Ltd, Ghatshila (Bihar, India) was carried out usingAspergillus niger culture filtrate. The effects of the duration of leaching, temperature, pulp density and the addition of hydrochloric acid were studied.A. niger culture filtrate solubilized metals from the converter slag at levels of 18.70% copper, 7.40% nickel and 4.00% cobalt. Addition of hydrochloric acid was found to improve copper, nickel and cobalt solubilization to 46.52, 27.90 and 37.96%, respectively. HPLC analysis of the fungal culture filtrate revealed the presence of succinic and citric acids. Therefore, leaching of the slag was also carried out with matching concentrations of these organic acids individually as well as with both mixed together. Results are discussed.

Field Duration of Chlorsulfuron Bioactivity in the Central Great Plains

AbstractThe duration of chlorsulfuron {2‐chloro‐N [(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2‐yl)aminocarbonyl]benzenesulfonamide} bioactivity in Central Great Plains soils was determined by measuring the influence of several environmental factors on chlorsulfuron degradation. Chlorsulfuron was applied at 35 and 70 g ha−1 to four soils: Platner sandy loam and Weld (Aridic Paleustolls) loam at Akron, CO; Roxbury (Cumulic Haplustoll) silt loam at Jetmore, KS; and Rosebud (Aridic Argiustolls) sandy loam at Chugwater, WY. Soil pH, organic matter level, number of precipitation events >0.25 cm, and leaching were the major environmental factors influencing chlorsulfuron duration of bioactivity. A chlorsulfuron rate × soil × year interaction occurred, but this interaction was not consistent over all soils. A model developed for predicting chlorsulfuron duration of bioactivity would be more accurate if designed for soils with similar organic matter levels, as organic matter level influenced duration of bioactivity and leaching of chlorsulfuron. Chlorsulfuron leaching was also affected by soil type and year of study. In greenhouse bioassay studies, sunflower (Helianthus annuus L.) did not differ from corn (Zea mays L.) in sensitivity to chlorsulfuron residues in soil.

A ferrous chloride-oxygen leach process for nickel-copper sulphide concentrations

This paper describes a ferrous chloride-oxygen leach process for recovery of nickel and copper values from sulphide concentrates available in India. The sulphide concentrates aareleached with a stirred solution of ferrous chloride in a glass-lined reactor operated at various temperatures and oxygen pressures. In this single step process, copper and nickel are converted into their water soluble chloride forms, whereas iron is rejected as hydrated iron oxide with simultaneous generation of sulphur in the non-polluting elemental form. The influence of various parameters such as (i) amount of ferrous chloride (60–100% stoichiometric), (ii) oxygen pressure (0.308–0.515 MPa), (iii) leaching temperature (90–120°C) and (iv) duration of leaching (2–10 h) on the leaching process has been examined. It has been possible to recover 94–99% nickel and 98% copper with low iron contamination by using optinum conditions, such as a stoichiometric amount of ferrous chloride, a temperature of 110°C, an oxygen pressure of 0.377 MPa and a duration of 8 h.

A Uraniferous Granite in Central Texas: ABSTRACT

The Precambrian Oatman Creek granite exposed in Gillespie County, central Texas, contains 5 to 10 times more uranium than that of an average granite. Samples of this granite, collected from outcrops and quarry openings, were studied by petrographic, delayed neutron counting, fission track, and gamma-ray spectrometry methods. Experiments of leaching uranium from disaggregated samples were also made. The granite is medium grained with an average composition of 36% quartz, 25% K-feldspar, 38% plagioclase, and 1% biotite and others. In an 80-acre (32 ha.) outcrop area 32 samples, most of which have some uranium removed from weathering, show an average uranium content of 25 ppm; relatively unweathered samples have 50 to 100 ppm uranium. Most uranium occurs between grain boundaries which is called intergranular uranium; some occurs in microfractures developed during late, hydrothermal stages. A portion of the uranium also occurs in discrete minerals, particularly oxides of iron or iron-titanium, and accessory minerals such as zircon, sphene, garnet, and others. This distribution indicates that much of the uranium mineralization was a result of deuteric or hydrothermal activities. Selected acids of various concentrations were used in experimental leaching of uranium from Oatman Creek granite. Other variables in the experiments were degree of disaggregation and duration of leaching. The results indicate that more than two thirds of the uranium can be leached in a few hours time from the granite without excessive grinding, when a 5N acid is used. This study shows that the Oatman Creek granite may be a long-term source of uranium in the future. End_of_Article - Last_Page 441------------

Reduction-roasting and ferric chloride leaching of copper converter slag for extracting copper, nickel and cobalt values

In a previous investigation the optimum conditions for recovering copper, nickel and cobalt from converter slag through ferric chloride leaching have been described. The study of various parameters revealed that nickel and cobalt recovery could not be improved beyond 24 to 26% respectively from converter slag, though more than 90% of the copper could be extracted. Further attempts were made to bring the metal values completely into solution through reduction-roasting followed by ferric chloride leaching of the slag. The present work comprises a study of various experimental conditions such as concentration of ferric chloride, duration of leaching, duration of reduction-roasting, temperature and nature of reducing agent, to arrive at the optimal recovery of the metal. Under identical experimental conditions a decrease in copper recovery, but an increase in nickel and cobalt recovery has been observed above a roasting temperature of 750°C. The decrease in copper recovery has been attributed to copper ferrite formation which has been confirmed both by leaching experiments with synthetic mixtures and by X-ray diffraction studies with both slag samples and synthetic mixtures. Recovery of nickel has also shown little decline when solid reductants were used above 850°C whereas cobalt recovery remains nearly the same even above 850°C. Under optimum conditions 80% copper, 95% nickel and 80% cobalt could be recovered by reducing the slag at 850°C with 10 wt % furnace oil, followed by leaching with ferric chloride.

Preparation of titania from llmenite by selective H2S sulfidization

Experiments on preferential sulfidization of ilmenite in a static bed by hydrogen sulfide gas with a flow rate of about 20 cu cm per min were conducted at 800°, 900°, 1000°, and 1100°C for different periods. Sulfidization (conversion of about 95 pct of the iron to its sulfide) at 1000°C for 5 hr or at 1100°C for 4 hr was considered quite suitable. The sulfidized samples were leached with boiling dilute hydrochloric acid and the influence of the concentration, amount of the acid, and the duration of leaching was studied. Leaching was most effective by employing 20 pct excess 2 N boiling hydrochloric acid for 1/2 hr. By this treatment, about 95 pct of the iron in ilmenite could be removed and a residue containing about 91 pct TiO2 has been obtained. X-ray analysis revealed that TiO2 in the residue has rutile structure. The merits of the process for commercial utilization have been mentioned briefly.