Oxygen application to chloride leaching of complex sulfide ores

The study investigates leaching of complex sulfide ores with simultaneous regeneration of the leaching solution and removal of dissolved iron to balance the iron concentration in the leaching process. To minimize environmental pollution and obtain high metal extraction from the ores, leaching with a ferric chloride solution is adapted to treat Delta sulfide ores. The experimental results indicate that under high oxygen pressure leaching, oxidation of ferrous ion to ferric ion and partial precipitation of iron from solution can occur simultaneously. However, the findings also indicate that leaching the ores with simultaneous iron precipitation in one operation is difficult. It is better to precipitate excess iron in one stage; then leach the ores in another stage using the regenerated leaching solution

Nitrate leaching from arable crop rotations in organic farming

Nitrate leaching from crop rotations for organic grain production were investigated in a field experiment on different soil types in Denmark from 1997 to 2002. Three experimental factors were included in the experiment in a factorial design: 1) proportion of grass-clover and pulses in the rotation, 2) cover crop (with and without), and 3) manure (with and without). Two four-course rotations were compared. They had one year of grass-clover as a green manure crop, either followed by spring wheat or by winter wheat. The nitrate leaching was measured using ceramic suction cells. The nitrate leaching did not differ between the rotations, as a change in leaching following the grass-clover was compensated by a reverse effect in the grain crops. Use of cover crops reduced N leaching by 23 to 38% at crop rotation level with the highest reduction on the coarse sandy soil. Simulation of N leaching using the FASSET model showed that a practice of using part of the summer period in the grass-clover as a bare fallow to control couch grass could increase leaching substantially, in particular on the sandy soil

In field N transfer, build-up, and leaching in ryegrass-clover mixtures

Two field experiments investigating dynamics in grass-clover mixtures were conducted, using 15N- and 14C-labelling to trace carbon (C) and nitrogen (N) from grass (Lolium perenne L.) and clover (Trifolium repens L. and Trifolium pratense L.). The leaching of dissolved inorganic nitrogen (DIN), as measured in pore water sampled by suction cups, increased during the autumn and winter, whereas the leaching of dissolved organic nitrogen (DON) was fairly constant during this period. Leaching of 15N from the sward indicated that ryegrass was the direct source of less than 1-2 percent of the total N leaching measured, whereas N dynamics pointed to clover as an important contributor to N leaching. Sampling of roots indicates that the dynamics in smaller roots were responsible for N and C build-up in the sward, and that N became available for transfer among species and leaching from the root zone. The bi-directional transfer of N between ryegrass and clover could however not be explained only by root turnover. Other processes like direct uptake of organic N compounds, may have contributed

Leaching Properties of Estuarine Harbor Sediment Before and After Electrodialytic Remediation

Electrodialytic remediation (EDR) can be used to extract heavy metals from a variety of different media. In this work, contaminated harbor sediments from two locations in the United States and one in Norway were subjected to EDR, and were compared with batch extractions conducted with the sediment. pH-dependent leaching tests were used to evaluate changes in leaching properties of treated and control sediments. Significant fractions of total concentrations were removed during treatment (35–95% with an average of 75% for all sediments and elements investigated). The release of elements in pH-dependent leaching tests, however, demonstrated equal or greater leaching from treated sediments in the neutral pH range. Dissolved organic carbon appears to be a significant contributor to post-treatment increases in leaching, and dissolution of significant iron and aluminum sorption sites is hypothesized to also play a role. This research highlights the importance of understanding contaminant speciation and availability, as total metals concentrations, in this particular case, do not relate to estimates of the environmental availability of metals (total concentrations were typically two to three orders of magnitude greater than concentrations released during pH-dependent leaching)

Contributions to predicting contaminant leaching from secondary materials used in roads

Slags, coal ashes, and other secondary materials can be used in road construction. Both traditional and secondary materials used in roads may contain contaminants that may leach and pollute the groundwater. The goal of this research was to further the understanding of leaching and transport of contaminants from pavement materials. Towards this goal, a new probabilistic framework was introduced which provided a structured guidance for selecting the appropriate model, incorporating uncertainty, variability, and expert opinion, and interpreting results for decision making. In addition to the framework, specific contributions were made in pavement and embankment hydrology and reactive transport, Bayesian statistics, and aqueous geochemistry of leaching. Contributions on water movement and reactive transport in highways included probabilistic prediction of leaching in an embankment, and scenario analyses of leaching and transport in pavements using HYDRUS2D, a contaminant fate and transport model. Water flow in a Minnesota highway embankment was replicated by Bayesian calibration of hydrological parameters against water content data. Extent of leaching of Cd from a coal fly ash was estimated. Two dimensional simulations of various scenarios showed that salts in the base layer of pavements are depleted within the first year whereas the metals may never reach the groundwater if the pavement is built on adsorbing soils. Aqueous concentrations immediately above the groundwater estimated for intact and damaged pavements can be used for regulators to determine the acceptability of various recycled materials. Contributions in the aqueous geochemistry of leaching included a new modeling approach for leaching of anions and cations from complex matrices such as weathered steel slag. The novelty of the method was its simultaneous inclusion of sorption and solubility controls for multiple analytes. The developed model showed that leaching of SO4, Cr, As, Si, Ca, Mg, and V were controlled by corresponding soluble solids. Leaching of Pb was controlled by Pb(VO4)3 solubility at low pHs and by surface precipitation reactions at high pHs. Leaching of Cd and Zn were controlled by surface complexation and surface precipitation, respectively

Removal of Cyanides from Gadung (Dioscorea hispida Dennst.) Tuber Chips using Leaching and Steaming Techniques

Gadung (Dioscorea hispida Dennst.) has been considered as one of staple foods in Indonesia. However, its high cyanides content has limited its utilisation for commercial food production. This work is aimed to investigate the removal of cyanides content from gadung tuber chips through two consecutive treatments, i.e. leaching and steaming and to propose mathematics model for the leaching process. The results showed that processing water flow rate and leaching time affected the efficiency of cyanides removal in the leaching process. The proposed mathematical model was able to represent the removal of cyanides through leaching process very well. The cyanides content removal was also found to be affected by steaming time. Best processing condition was at leaching using 5.00 10-5 m3.s-1 for 3,600 s, followed by steaming for 3,600 s to obtain cyanides content of 29.9 mgkg-1. While the yielded gadung tuber chips are considered as safe for consumption, further research on physicochemical characteristic of the gadung tuber flour is necessary for its utilisation consideration

Effect of clay amendments on nitrogen leaching and forms in a sandy soil

Nitrogen (N) leaching in sandy soil decreases fertiliser use efficiency and may depress plant production. Application of high cation exchange capacity (CEC) materials (e.g. high activity clay minerals) is hypothesized to reduce N leaching and increase plant N uptake in sandy soils. However, the mechanism of leaching in sands with clay amendment is not understood. A column experiment was conducted to determine N leaching and N concentration in soil solution in a sandy soil (1.4 % clay) with three soil amendments (nil, clay soil and bentonite clay) and three fertiliser rates (0, 28 N 17 P 22 K kg/ha and 56 N 34 P 44 K kg/ha). Soil amendments were applied at the rate of 50 Mg/ha. The soil columns were leached with de-ionised water equivalent to 50 mm rainfall every 4 days. Concentrations of soil solution extracted by Rhizon samplers indicated that NH4 leaching was decreased 38-43 % by bentonite addition but little of the soil solution N was in NO3 form and bentonite had no effect on mobility of this form of N. The application of bentonite was able to hold NH4 in soil solution of top soil. Leaching of NH4 was delayed to 15 day after fertiliser application in bentonite-amended sand

Catch crop strategy and nitrate leaching following grazed grass-clover

Cultivation of grassland presents a high risk of nitrate leaching. This study aimed to determine if leaching could be reduced by growing spring barley (Hordeum vulgare L.) as a green crop for silage with undersown Italian ryegrass (Lolium multiflorum Lam.) compared with barley grown to maturity with or without an undersown conventional catch crop of perennial ryegrass (Lolium perenne L.). All treatments received 0,60 or 120 kg of ammonium-N ha-1 in cattle slurry. In spring 2003, two grass-clover fields (3 and 5 years old, respectively, with different management histories) were ploughed. The effects of the treatments on yield and nitrate leaching were determined in the first year, while the residual effects of the treatments were determined in the second year in a crop of spring barley⁄perennial ryegrass. Nitrate leaching was estimated in selected treatments using soil water samples from ceramic cups. The experiment showed that compared with treatments without catch crop, green barley⁄Italian ryegrass reduced leaching by 163–320 kg Nha-1, corresponding to 95–99%, and the perennial ryegrass reduced leaching to between 34 and 86 kg Nha-1, corresponding to a reduction of 80 and 66%. Also, in the second growing season, leaching following catchcrops was reduced compared with the bare soil treatment. It was concluded that the green barley⁄Italian ryegrass offers advantages not only for the environment but also for farmers, for whom it provides a fodder high in roughage and avoids the difficulties with clover fatigue increasingly experienced by Danish farmers

Leaching of organic nitrogen and carbon after cultivating grass-clover pastures

Leaching of organic nitrogen (DON) and carbon (DOC) was measured after cultivating grass-clover of different age. It was found that DON and escpecially DOC was lost in considerable amounts, and that the leaching depends upon crop and management. The highest concentrations of DON were measured in the bare soil treatment, whereas concen-trations in catch crop treatments were between 1.2 and 3.2 mg N L-1. The leaching of DOC showed opposite trends compared to leaching of DON with higher values in the catch crop treatments (296 - 310 kg DOC ha-1) than in bare soil treatments (174 - 217 kg DOC ha-1)

Estimated N leaching losses for organic and conventional farming in Denmark

The impact of organic compared to conventional farming practices on N leaching loss was studied for Danish mixed dairy and arable farms using an N balance approach based on representative data. On mixed dairy farms a simple N balance method was used to estimate N surplus and N leaching loss. On arable farms the simple N balance method was unreliable due to changes in the soil N pool. Consequently, the FASSET simulation model was used to estimate N surplus, N leaching loss and the changes in the soil N pool. The study found a lower N leaching loss from organic than conventional mixed dairy farms, primarily due to lower N inputs. On organic arable farms the soil N pool was increasing over years but the N leaching loss was comparable to conventional arable farms. The soil N pool was primarily increased by organic farming practices and incorporation of straw. The highest increase in the soil N pool was seen on soils with a low level of soil organic matter. The level of N leaching loss was dependent on soil type, the use of catch crops and the level of soil organic matter, whereas incorporation of straw had a minor effect. N leaching was highest on sandy soils with a high level of soil organic matter and no catch crops. The study stresses the importance of using representative data of organic and conventional farming practices in comparative studies of N leaching loss