Column Leaching Experiments Research Articles

Physicochemical properties and heavy metals leachability of fly ash from coal-fired power plant

The physicochemical properties of fly ash from two kinds of coal-fired power plants were studied. Three aspects were examined: the micro-morphology, the mineral composition and the content of heavy metals. The results show that the fly ash from plants using a circulating fluidized bed are more irregular particles, while the particles from the plants using a pulverized coal-fired boiler are mainly spherical in shape. Quartz and mullite are the main crystalline phases in the ash. Clearly, both the technology and the coal used by a power plant can influence the mineral composition of the ash. The mineral composition of fly ash from a circulating fluidized bed is more complex than that from a pulverized coal-fired boiler. The quantity of elements found in the fly ash is greater than that found in the bottom ash for the same plant. Heavy metals are likely to be enriched in the fly ash. Heavy metal leachability was studied using two leaching methods. The results indicate that most of the heavy metals that leached during either batch leaching or column leaching experiments did not exceed the related maximum concentration standards. But Ni concentrations in the leachates from both batch and column tests exceed the standard. The highest excess rates in both tests were 572% and 497%, which levels might threaten the environment.

Roles of vegetation, flow type and filled depth on livestock wastewater treatment through multi-level mineralized refuse-based constructed wetlands

The treatment efficiencies of mineralized refuse-based constructed wetlands (MRCWs) for livestock wastewater have been investigated through a series of laboratory-scale experiments over a period of 180 days from summer to winter. Four wetland plant species ( Cyperus alternifolius, Phragmites spp., Canna indica and Acorus calamus) were grown as monocultures in individual MRCWs and their effect on wastewater treatment by mineralized refuse particles was monitored. It was found that the presence of vegetation caused only minor variations in the efficiency of removing chemical oxygen demand (COD Cr), suspended solids (SS), ammonia nitrogen (NH 3-N), total phosphorus (TP) and total nitrogen (TN) from livestock wastewater. Single-stage MRCWs were integrated to organize combined CWs system to investigate the inlet flow type on pollutants removal efficiency. Three-level/stage MRCWs were then designed to be used without vegetation to treat livestock wastewater by the horizontal-flow (ladder-type system) and vertical-flow (tower-type system). The removal rates of pollutants were observed to be directly proportional to the number of levels or stages in the MRCWs. The average removal rates for three-level tower-type MRCWs were 62.4 ± 11.2% ( P < 0.01) for COD Cr, 86.5 ± 6.7% for SS, and >95% for NH 3-N and for TP under vertical flow that are slightly higher than the removal rates for the three-stage ladder-type horizontal flow MRCWs in long-term operation. The high removal rate of COD Cr and strong nitrification ability of MRCWs result in a much lower stoichiometric ratio of COD Cr:nitrate nitrogen (NO 3 −-N) at the outlets, which caused a shortage of carbon for subsequent denitrification. A leaching column experiment was conducted with 150 cm-deep mineralized refuse to evaluate its denitrification effect on a synthetic solution having a low ratio of COD Cr:NO 3 −-N. More than 95% of the NO 3 −-N content was removed for column depths between 120 cm and 150 cm, the mineralized refuse particles themselves serving as a carbon source. The integrated system of anaerobic storage tank, multi-level/stage MRCWs and an MR-filled column in series is therefore recommended for livestock wastewater treatment, with C. alternifolius and/or C. indica being planted.

Production and dissolution rates of earthworm-secreted calcium carbonate

Abstract Earthworms secrete granules of calcium carbonate. These are potentially important in soil biogeochemical cycles and are routinely recorded in archaeological studies of Quaternary soils. Production rates of calcium carbonate granules by the earthworm Lumbricus terrestris L. were determined over 27 days in a range of soils with differing chemical properties (pH, organic matter content, water holding capacity, bulk composition, cation exchange capacity and exchangeable cations). Production rate varied between soils, lay in the range 0 – 0.043 mmol CaCO 3 (0–4.3 mg) earthworm−1 d−1 with an average rate of 8 × 10 − 3 mmol CaCO 3 (0.8 mg) earthworm−1 d−1 and was significantly correlated (r = 0.68, P ≤ 0.01) with soil pH. In a second experiment lasting 315 days earthworms repeatedly (over periods of 39–57 days) produced comparable masses of granules. Converting individual earthworm granule production rates into fluxes expressed on a per hectare of land per year basis depends heavily on estimates of earthworm numbers. Using values of 10–20 L. terrestris m−2 suggests a rate of 18 – 3139 mol CaCO 3 ha − 1 yr − 1 . Data obtained from flow-through dissolution experiments suggest that at near neutral pH, granule geometric surface area-normalised dissolution rates are similar to those for other biogenic and inorganic calcites. Fits of the data to the dissolution relationship r = k(1 − Ω)n where r = dissolution rate, k = a rate constant, Ω = relative saturation and n = the reaction order gave values of k = 1.72 × 10−10 mol cm−2 s−1 and n = 1.8 for the geometric surface area-normalised rates and k = 3.51 × 10−13 mol cm−2 s−1 and n = 1.8 for the BET surface area-normalised rates. In 196 day leaching column experiments trends in granule dissolution rate referenced to soil chemistry corresponded to predictions made by the SLIM model for dissolution of limestone in soil. If soil solution approaches saturation with respect to calcium carbonate, granule dissolution will slow or even stop and granules be preserved indefinitely. Granules have the potential to be a small but significant component of the biogeochemical cycling of C and Ca in soil.

Adsorption and mobility of aromatic arsenicals in Japanese agricultural soils

We investigated the adsorption and mobility of aromatic arsenicals (AAs) in two types of Japanese agricultural soils in batch and column leaching experiments. The amounts of AAs adsorbed onto a Fluvisol (a sandy loam) and an Andosol (a light clay) decreased in the order of phenylarsonic acid (PAA) > methylphenylarsinic acid (MPAA) > diphenylarsinic acid (DPAA) > methyldiphenylarsine oxide (MDPAO) > dimethylphenylarsine oxide (DMPAO). The amounts of all AAs adsorbed onto the Andosol, which had more amorphous minerals and organic carbon, were higher than those adsorbed onto the Fluvisol. The adsorbability of AAs increased with both an increasing arsenate proportion and a decreasing hydrophobicity. This result suggests that the mechanisms of adsorption of AAs onto soil are due mainly to ligand exchange reactions and less to hydrophobic interactions. Mobility in the Fluvisol decreased in the order of DMPAO (30 cm) > MDPAO (25 cm) > MPAA (20 cm) > DPAA (15 cm) = PAA (15 cm). Mobility in the Andosol was less: DMPAO (15 cm) = MDPAO (15 cm) > DPAA (10 cm) > MPAA (5 cm) = PAA (5 cm). The mobility of MDPAO and DMPAO was higher than that of PAA and MPAA, and all AAs were less mobile in the Andosol than in the Fluvisol.

Phosphorus leaching in a calcareous soil treated with plant residues and inorganic fertilizer

AbstractColumn experiments were conducted over 45 d to determine the degree of P mobility. The sandy loam soil was spiked with 200 mg P kg–1 and 5% organic residues. The treatments included: control without any water‐soluble P and plant residues, potato, wheat, water‐soluble P fertilizer, wheat + water‐soluble P, and potato + water‐soluble P. Each column was leached with distilled water, and leachates were collected and analyzed for P, K+, Ca2+, Mg2+, along with pH and EC. Sequential extraction was performed on soil samples at the end of leaching column experiments. The relatively high initial concentration of P in the leachates decreased to more stable values after 15 d which can be attributed to the colloid‐bound P. The P concentrations in the leachates fluctuated between 8 and 220 mg L–1 in the water‐soluble–P fertilizer treatment, between 0.80 and 230 mg L–1 in the potato + water‐soluble‐P treatment, and between 0.90 and 214 mg L–1 in the wheat + water‐soluble P treatment. Leaching loss of P mainly occurred in the 15 d of leaching, accounting for 94%, 88%, and 65% of total P leached in wheat + water‐soluble‐P, potato + water‐soluble‐P, and water‐soluble‐P treatments, respectively. Maximum amount of P leached was found from an exponential kind model and was in the range 0.45 mg kg–1 to 125.4 mg kg–1 in control and potato + water‐soluble‐P treatments, respectively. Sequential extraction results showed that in control and amended soils the major proportion of P was associated with Ca. The leachate samples in all treatments were saturated with respect to hydroxyapatite, β‐tricalcium phosphate, and octacalcium phosphate up to 20 d of leaching, whereas they were undersaturated with respect to Mg‐P minerals through the entire leaching experiment.

Immobilization of copper in contaminated sandy soils using calcium water treatment residue

Chemical remediation has attracted increasing attention for heavy metal contaminated soils because of its relatively low cost and high efficiency. In this study laboratory incubation and column leaching experiments were conducted to understand the mechanisms of copper (Cu) immobilization by calcium water treatment residue (Ca-WTR) and to estimate the optimal rate for remediating Cu-contaminated soils. The results showed that Ca-WTR amendment significantly raised soil pH and decreased water soluble and exchangeable Cu by 62–90% in the contaminated soils. Most of the bioavailable Cu was converted into more stable Cu fractions, i.e. oxides-bound and residual Cu. The cumulative amount of Cu in the leachate after 10 leaching events was reduced by 80% and 73%, respectively for the two tested soils at the Ca-WTR rate of 20 g kg −1 for Alfisol and 100 g kg −1 for Spodosol. These results indicate that Ca-WTR is effective in raising soil pH and converting labile Cu to more stable forms in the contaminated soils. A pH value of 6.5 was found to be critical for lowering Cu availability in the soils. Based on this criterion and pH response curve to Ca-WTR application, the optimal rates of Ca-WTR can be estimated for different Cu-contaminated soils.

Influence of the Soil/Solution Ratio, Interaction Time, and Extractant on the Evaluation of Iron Chelate Sorption/Desorption by Soils

Synthetic Fe chelates are the most efficient agricultural practice to control Fe deficiency in crops, EDTA/Fe3+ and o,o-EDDHA/Fe3+ being the most commonly used. Their efficacy as Fe sources and carriers in soils can be severely limited by their retention on it. The aim of this work is to evaluate the possible bias introduced in the studies of the iron chelate retention by soils. For that purpose, results obtained for EDTA and EDDHA iron chelates from two batch studies with different soil/solution ratios were compared with data obtained for a leaching column experiment. Moreover, different extractants were tested to study the o,o-EDDHA/Fe3+ and o,p-EDDHA/Fe3+ desorption from a calcareous soil, and also the effect of the interaction time in their retention process has been evaluated. In summary, the mobility through a calcareous soil of the studied iron chelates differs greatly depending on the type of iron chelate and also on the procedure used to evaluate the retention and the soil/solution ratio used. In general, the leaching column method is preferred because the achieved conclusions are more representative of the natural conditions, but batch methods are very useful as a preliminary experiment, especially one with a high soil/solution ratio. The iron chelate desorption could be quantified by using a sequential extraction with water, sodium sulfate, and DTPA as extractants. Under the experimental conditions used in this study, o,o-EDDHA/Fe3+ retention increased with interaction time.

Leaching Characteristics of Arsenic from Aged Alkaline Coal Fly Ash Using Column and Sequential Batch Leaching

Leaching of arsenic from ash in coal fly ash disposal facilities is a cause for concern due to possible contamination of groundwater. Sequential batch and column leaching experiments were carried out to determine the leaching of arsenic from ash found at a retired ash impoundment basin near a coal-fired power plant. This study assessed the leaching characteristics of arsenic from aged alkaline coal fly ash as a function of ash properties and ash depth. Comparable levels of arsenic leached from the ash in column leaching (10.5%) and sequential batch leaching (11.1%) after 14 days (7 stages) of leaching, while less arsenic (17.8%) leached for column leaching than for sequential leaching (22.0%) after 42 days (21 stages) of leaching. The leaching characteristics of arsenic in column leaching and sequential batch leaching were similar, where more than half of the leaching of arsenic occurred within 14 days of leaching with the maximum leaching of arsenic occurring during the second and third stages of leaching. More arsenic leached from the deeper ash samples in sequential batch leaching of ash samples from various depths. Arsenic leached out mainly as calcium hydrogen arsenate from the calcium arsenate present in ash. The short-term (2-day) leaching of arsenic from ash was limited by the solubility of calcium arsenate, while the long-term leaching of arsenic was limited by the leaching of calcium bicarbonate which controlled the leachate pH. The source of calcium bicarbonate in the leachate was the amorphous calcium carbonate in the ash.

Use of surfactant-modified zeolite to carry and slowly release sulfate

Use of water soluble fertilizers could result in increased loss of plant nutrient during irrigation and cause non-point source groundwater contamination. In this study the feasibility of using surfactant-modified zeolite (SMZ) as fertilizer additives to control sulfate release was tested in batch and column leaching experiments. The zeolite was able to carry as much as 5, 15, and 25 mmol/kg of sulfate when modified to 100%, 150% and 200% of its external cation exchange capacity (ECEC). Batch tests showed an almost instantaneous and partially reversible sulfate release. Leached with 50 pore volumes (PVs) of water, 70% and 85% of the loaded sulfate was still remained on SMZ modified to 150% and 200% ECEC, respectively. The initial sulfate concentration in leachate was reduced by a factor of three when sulfate loaded SMZ was used compared to mixtures of soluble sulfate and zeolite of the same loading in column leaching experiments. Mass balance showed a 31% recovery after the columns were flushed with 60 PVs of water, similar to the observation in batch tests. The results indicated that SMZ could be a good carrier for sulfate. Thus, leaching of sulfate can be greatly reduced and slow release of sulfate can be achieved if SMZ is used as fertilizer additives.

Transport and interaction of arsenic, chromium, and copper associated with CCA-treated wood in columns of sand and sand amended with peat

Laboratory column leaching experiments were conducted to investigate the transport and interaction of As, Cr, and Cu associated with CCA-treated wood in sand with and without peat amendment. Results showed that leaching behavior of As, Cr, and Cu in these substrates were totally different. Substrate characteristics and microorganism activity posed distinct effects on the transport and transformation of these three elements. Arsenic was rapidly leached out from the columns with or without the amendment of peat, while Cr remained in all columns during the entire experimental period (215 d). Copper was leached out only in the substrate column without peat. The presence of microorganism clearly facilitated the transport of As, while it did not show obvious effects on the transport of Cr and Cu. Interactions among these three elements were observed during the processes of adsorption and transport. The adsorption of Cu on soil was enhanced with the adsorption of As, likely caused by a more negatively charged soil surface because of As adsorption. The adsorption of Cr on soil increased the adsorption of As due to the additional As binding sites induced by Cr adsorption. These results suggest that As concentrations in the soil affected by CCA-treated wood could largely exceed predictions based on soil adsorption capacity for As. The evaluation of the impact on human health associated with CCA-treated wood should take consideration of the distinct transport characteristics of three elements and their interactions in soils.

Potential nitrogen and phosphorus leaching from soils fertilized with meat and bone meal

The nitrogen and phosphorus contents of meat and bone meal (MBM) make it a potentially valuable nutrient source in agriculture. Its narrow N:P ratio, however, makes it a potential environmental risk if it is not utilized with caution. A column-leaching experiment was conducted to assess potential nitrogen and phosphorus leaching from bare soils fertilized with MBM. This should give an idea of the efficacy of autumn or early spring MBM application on land devoid of vegetation cover. Earlier greenhouse and field experiments have indicated that nitrogen mineralization after MBM application takes place relatively rapidly. The column experiment conducted here has indicated that spring application of MBM prior to planting can result in the loss of mineral nitrogen, reducing the total amount of N available to the crop. A higher initial loss (up to 47 mg l−1) of ammonium was found for the MBM treated soils, but this declined to less than 0.1 mg l−1 by the end of the experiment, 11 weeks later. Nitrate loss was highest at the onset of the experiment for the soils that received mineral N fertilizer. With time, however, the largest nitrate losses were associated with the MBM-treated soils. Nitrate leaching continued to well beyond the end of the experiment. The effect will most certainly be exacerbated when the crop N (rather than crop P) requirement forms the basis for MBM application. The amount of P leached as ortho-P is probably small but may also represent an environmental risk if N remains to be the basis of MBM application. Based on the results presented here and considering the dangers of elevated nutrient losses, autumn and early spring MBM application may not be recommended.

Mercury mobility in mine waste from Hg-mining areas in Almería, Andalusia (Se Spain)

Mining wastes and calcines from two abandoned mining areas (Valle del Azogue and Bayarque in Almería) have been characterized. In the mining wastes, the dominant mercury phases are cinnabar and elemental mercury in the matrix. In the calcines, however, the dominant mercury phase is elemental mercury bounded to the matrix. Water-leaching experiments were conducted on low-grade stockpiles and calcines in order to simulate the mobilization of mercury by runoff under environmental conditions. The laboratory column-leaching experiments show a possible mobilization of mercury from Hg 0 dissolution, colloid transport and a possible dissolution of calomel and other soluble phases in the mine wastes from the Valle del Azogue and Bayarque mines. Equilibrium speciation modeling of Hg, conducted using the numerical code MINTEQ, showed that the theoretical dominant mercury species in the calcine and mining wastes samples are Hg(OH) 2, HgCl 2, HgClOH and Hg 0. In some leachates obtained from the Valle del Azogue mining wastes (sample A06), the high Hg concentrations may indicate the possible dissolution of mineral phases such as calomel and other soluble phases, which are subsaturated. The environmental results indicate a great environmental mobility of mercury, especially during wet episodes associated with intense precipitation events, when there are significative amounts of secondary soluble minerals.

Fly‐Ash‐Amended Sand as Filter Media in Bioretention Cells to Improve Phosphorus Removal

This study identified material with high phosphorus sorption suitable for bioretention filter media. Materials examined were fly ash, two expanded shales, peat moss, limestone, and two common Oklahoma soils--Teller loam and Dougherty sand. The peat moss was a phosphorus source, while the two soils, limestone, and one expanded shale had only modest sorption capacity. One expanded shale and the fly ash had significant phosphorus sorption. Fly ash is unsuitable for use in a pure form, as a result of its low permeability, but phosphorus sorption on the sand was increased significantly with the incorporation of small amounts of fly ash. Column leaching experiments found that the sand with 2.5 and 5% fly ash and the better expanded shale had linear, non-equilibrium transport retardation factors of 272, 1618, and 185, with first-order rate coefficients of 0.153, 0.0752, and 0.113 hour(-1), respectively. Desorption experiments showed that the phosphorus sorption on the sand/fly ash mixture is largely nonreversible. Transport simulation assuming a 1-m-deep sand/fly ash treatment layer, with 5% of the watershed area, showed that the sand/fly ash filter media could effectively treat 1 mg/L influent for 12 years in a paved watershed and 34 years in a grassed watershed before exceeding Oklahoma's scenic rivers' phosphorus criterion of 0.037 mg/L. Significant phosphorus removal would continue for over 100 years.

Optimization of Chelator-Assisted Phytoextraction, Using EDTA, Lead and Sedum alfredii Hance as a Model System

Pot and leaching column experiments were conducted to optimize chelator-assisted phytoextraction of lead (Pb) from contaminated soils. Optimum phytoextraction occurred at added EDTA concentration of 5 mM in single dose for 10 days in low Pb soil (treated with 400 mg kg(-1) soil), while it would be better for high Pb soil (treated with 1,200 mg kg(-1) soil) with five intermittent doses of 10 mM EDTA for 7 days. Combined with column experiment, it could be inferred that chelator-assisted phytoextraction is more suitable for the slightly contaminated soils.

Enhancement of Heavy Metals Retention in Sandy Soil by Amendment with Fly Ash

Stormwater runoff from urban areas can transport a significant load of heavy metals. Thus, the metals retention capacity of filter media in stormwater infiltration systems, such as bioretention cells, is an important consideration. Batch sorption and column leaching experiments were conducted to determine the sorption of copper, lead, and zinc in three soils (Dougherty sand, Teller loam, and Slaughterville loam), fly ash, and fly ash/sand mixtures. Dougherty sand had the lowest heavy metals retention, while fly ash had the highest. The addition of fly ash to Dougherty sand greatly increased its heavy metals retention. Heavy metals transport in bioretention cells was modeled using a linear equilibrium, convection-dispersion transport model with parameters determined from laboratory columns. The modeling results indicated that a treatment layer of filter media with 1 m depth will remove heavy metals from stormwater for only 10 years if pure sand is used, but metals removal will continue for over 900 years if a fly ash/sand mixture is used.

IMPROVED CHALCOPYRITE LEACHING THROUGH OPTIMIZATION OF REDOX POTENTIAL

In the leaching of chalcopyrite with sulphuric acid solutions, the copper extraction rate reaches a maximum at a given redox potential. This article reviews our studies on the determination of the optimum redox potential for chalcopyrite leaching. Shaking flask and column leaching experiments for a chalcopyrite concentrate were performed under various conditions and the results were analyzed using a normalized redox potential defined from a reaction model assuming the formation of an intermediate Cu2S from chalcopyrite. Factors, such as metal ion concentrations, solid/liquid ratio and the presence of iron-oxidizing bacteria, caused significant variations in the copper extraction versus time plots. However the copper extraction rate versus normalized redox potential plots were independent of the above factors and the copper extraction rate reached a maximum at the normalized redox potentials around 0.43. Converting the normalized redox potential to the solution redox potential gives the optimum redox potential for chalcopyrite leaching as a function of cupric and ferrous ion concentrations. This semi-empirical equation can be used to predict the optimum redox potential during leaching operation and is useful to design the redox-controlled heap leaching for chalcopyrite. Lors de la lixiviation de la chalcopyrite avec des solutions d’acide sulfurique, la vitesse d’extraction du cuivre atteint un maximum à un potentiel rédox donné. Cet article examine notre étude de la détermination du potentiel rédox optimal de lixiviation de la chalcopyrite. On a effectué, sous diverses conditions, des expériences d’agitation du flacon et de lixiviation en colonne d’un concentré de chalcopyrite et l’on a analysé les résultats en utilisant un potentiel rédox normalisé défini à partir d’un modèle de réaction assumant la formation d’une forme active intermédiaire Cu2S à partir de la chalcopyrite. Des facteurs, comme les concentrations de l’ion métal, le rapport solide/liquide et la présence de bactéries oxydantes du fer, avaient pour conséquence des variations importantes dans l’extraction du cuivre par rapport au temps. Cependant, la vitesse d’extraction du cuivre par rapport aux graphes du potentiel rédox normalisé était indépendante des facteurs ci-dessus et elle atteignait un maximum aux potentiels rédox normalisés autour de 0.43. La conversion du potentiel rédox normalisé en potentiel rédox de la solution donne le potentiel rédox optimal pour la lixiviation de la chalcopyrite en fonction de la concentration des ions cuivriques et ferreux. On peut utiliser cette équation semiempirique pour prédire le potentiel rédox optimal lors de l’opération de lixiviation et cette dernière est utile pour concevoir la lixiviation en tas de la chalcopyrite contrôlée par le rédox.

Use of amendments to reduce leaching loss of phosphorus and other nutrients from a sandy soil in Florida

Transport of P from agricultural land contributes to the eutrophication of surface waters. Soil amendment is considered one of the best management practices (BMPs) to reduce P loss from sandy soils. Laboratory column leaching experiments were conducted to evaluate the effectiveness of different soil amendments in reducing P leaching from a typical sandy soil in Florida. The tested amendments were CaCl2, CaCO3, Al(OH)3, cellulose, and mill mud, and applied at the rate of 15 g/kg for a single amendment and each 7.5 g/kg if two amendments were combined. Leaching was conducted every four days for 32 days, 250 mL of deionized water being leached for each column per leaching event. Leachates were collected from each leaching event and analyzed for reactive P, PO4-P, and macro and micro-elements. Except for the soils amended with CaCl2, or CaCl2+CaCO3, reactive P and PO4-P leaching losses mainly occurred in the first three leaching events. Phosphorus leaching from the soils amended with CaCl2 or CaCl2+CaCO3 was less but more persistent than that of other amendments. Reactive P leaching loss was reduced by 36.0% and 40.4% for the amendments of CaCl2, and CaCl2+CaCO3, respectively, as compared with chemical fertilizer alone, and the corresponding values for PO4-P were 70.8% and 71.9%. The concentrations of K, Mg, Cu, and Fe in leachate were also decreased by CaCl2 or CaCl2+CaCO3 amendment. Among the seven amendments, CaCl2, CaCO3, or their combination were most effective in reducing P leaching from the sandy soil, followed by cellulose and Al(OH)3, the effects of mill mud and mill mud + Al(OH)3 were marginal. These results indicate that the use of CaCl2, CaCO3, or their combination can significantly reduce P leaching from sandy soil, and should be considered in the development of BMPs for the sandy soil regions. Recommendations and Outlook. Most agricultural soils in south Florida are very sandy with minimal holding capacities for moisture and nutrients. Repeated application of fertilizer is necessary to sustain desired yield of crops on these soils. However, eutrophication of fresh water systems in this area has been increasingly concerned by the public. Losses of P from agricultural fields by means of leaching and surface runoff are suspected as one of the important non-point contamination sources. The benefits and effectiveness of soil amendment in reducing P losses from cropping production systems while sustaining desired crop yield need to be demonstrated. Calcium chloride, CaCO3, or their combination significantly reduce P leaching from sandy soil, and should be considered in the development of BMPs for the sandy soil regions.

Modelling DCD effect on nitrate leaching under controlled conditions

Effects of nitrogen losses through nitrate leaching are one of the major environmental issues worldwide. To determine the potential effect of dicyandiamide (DCD), a nitrification inhibitor, on the transformation of urea nitrogen and subsequent nitrate leaching, incubation and column leaching experiments were performed. Tokomaru silt loam soil was treated with urea, DCD, or urea plus DCD. A control was also used. In the laboratory incubation experiment, the conversion of urea to ammonium (i.e. ammonification process or urea hydrolysis) occurred within a day, thereby increasing the soil pH from 5.8 to 6.9. DCD did not affect the ammonification process. However, DCD did slow down the subsequent oxidation of ammonium to nitrate (i.e. nitrification process). The half-life time of ammonium in this soil was increased from 9 days for the urea treatment to 31 days for the urea + DCD treatment. The production of nitrate was 5 times slower when DCD was added. In the leaching experiments, half the columns were leached after 1 day of incubation (Day 1), the other half 7 days later (Day 7). For Day 1, no significant differences in nitrate leaching could be seen between the treatments, as the nitrification had not yet taken place. For Day 7, DCD decreased nitrate leaching by 71% with a corresponding decrease in nitrate-induced cation leaching, including ammonium. Thus, DCD seems to be effective in decreasing both ammonium and nitrate leaching, but its high solubility and thus mobility could be a limitation to its use. The convection–dispersion equation, including source–sink terms for nitrogen transformations, ammonification, and nitrification rate constants, and a factor for nitrification inhibition by DCD, accounting for degradation and efficiency of DCD, could be used reasonably well to simulate nitrate leaching from the column leaching experiments. However, model parameter values for nitrification rate, and efficiency and decay rate for DCD, were different from those obtained from the incubation experiments, which was probably because of the difference in water content of soil between the incubation and leaching experiments.

Evaluation of nitrate leaching from mine tailings amended with biosolids under Mediterranean type climate conditions

Mine tailings are difficult to revegetate due to the lack of organic matter, severe nutrient limitations, and potential metal toxicity. Biosolids has been shown to be favorable for improving properties of mine tailings. The rates of biosolids required to reclaim mine tailings (up to 250 dry t ha - 1 ) may produce conditions where significant amounts of nitrates can leach into groundwater. Leaching column experiments were conducted to determine the influences of biosolids placement and plant cover on nitrate leaching from biosolids-amended mine tailings. PVC columns packed with 7.7 kg of tailings were treated with 168 g of biosolids (approximately 270 kg mineral N ha - 1 ). Biosolids were either placed on the surface or mixed with the tailings and half of the columns were seeded with perennial ryegrass ( Lolium perenne, L.). Columns were drip irrigated at a rate of 758 mm of water y - 1 . This rate was twice the average precipitation for Central Chile. All leachates were collected weekly for up to 21 weeks and analyzed for nitrate, pH, electrical conductivity, and chemical oxygen demand. The electrical conductivity and nitrate concentration of percolates decreased with time, while the pH remained constant. In some cases the percolate had nitrate concentrations greater than the maximum amount allowed for human consumption (10 mg NO 3 – N 1 - 1 ). Vegetation cover and mixing the biosolids with tailings reduced NO 3 – N concentrations in the percolate.

Mobility and Distribution of Zinc, Cadmium and Lead in Calcareous Soils Receiving Spiked Sewage Sludge

Leaching column experiments were conducted to determine the degree of mobility and the distribution of zinc (Zn), cadmium (Cd), and lead (Pb) because of an application of spiked sewage sludge in calcareous soils. A total of 20 leaching columns were set up for four calcareous soils. Each column was leached with one of these inflows: sewage sludge (only for two soils), spiked sewage sludge, or artificial well water (control). The columns were irrigated with spiked sewage sludge containing 8.5 mg Zn l−1, 8.5 mg Cd l−1, and 170 mg Pb l−1 and then allowed to equilibrate for 30 days. At the end of leaching experiments, soil samples from each column were divided into 18 layers, each being 1 cm down to 6 cm and 2 cm below that, and analyzed for total and extractable Zn, Cd and Pb. The fractionation of the heavy metals in the top three layers of the surface soil samples was investigated by the sequential extraction method. Spiked sewage sludge had little effect on metal mobility. In all soils, the surface soil layers (0-1 cm) of the columns receiving spiked sewage sludge had significantly higher concentrations of total Zn, Cd and Pb than control soils. Concentration of the heavy metals declined significantly with depth. The mobility of Zn was usually greater than Cd and Pb. The proportion of exchangeable heavy metals in soils receiving spiked sewage sludge was significantly higher than that found in the control columns. Sequential extraction results showed that in native soils the major proportion of Zn and Pb was associated with residual (RES) and organic matter (OM) fractions and major proportion of Cd was associated with carbonate (CARB) fraction, whereas after leaching with spiked sewage sludge, the major proportion of Zn and Pb was associated with Fe-oxcide (FEO), RES, and CARB fractions and major proportion of Cd was associated with CARB, RES and exchangeable (EXCH) fractions. Based on relative percent, Cd in the EXCH fraction was higher than Zn and Pb in soils leached with spiked sewage sludge.