Dilute Acid Leaching Research Articles

Performance assessment of dilute-acid leaching to improve corn stover quality for thermochemical conversion

Lignocellulosic biomass is a sustainable energy source that can help meet the demand for biofuels in the United States. However, the quality and availability of such feedstocks greatly affect their suitability for downstream conversion. This work reports the effects of dilute-acid leaching at various aqueous loadings, temperatures and catalyst loadings (sulfuric acid) on the quality of a traditional biochemical feedstock, corn stover, as a potential feedstock for thermochemical conversions.At 95wt% aqueous, dilute-acid leaching was observed to effectively remove 97.3% of the alkali metals and alkaline earth metals that can negatively affect degradation pathways during pyrolysis and result in greater yield of non-condensable gases. In addition, up to 98.4% of the chlorine and 88.8% of the phosphorus, which can cause equipment corrosion and foul upgrading catalysts, respectively, were removed. At 25°C in the absence of the acid catalyst, only 6.8% of the alkali metals and alkaline earth metals were removed; however, 88.0% of chloride was still removed.The ratio of alkaline/acidic ash species has been suggested to proportionately relate to slagging in combustion applications. The initial alkali/acid ratio of the ash species present in the untreated corn stover was 0.38 (significant slagging risk). At 95wt% aqueous, this ratio was decreased to 0.18 (moderate slagging risk). At 0wt% catalyst and 90°C, the ratio was decreased to 0.07, 0.08 and 0.06 at 0.5wt% catalyst at 25°C, 50°C and 90°C, respectively (low slagging risk). Increasing the catalyst loading to 1.0% slightly decreased the measured alkali/acid ratio of remaining ash.The results presented here show that a water wash or a dilute-acid preprocessing step can improve corn stover quality for pyrolysis, hydrothermal liquefaction and combustion.

Recovery of Titanium Compounds from Ti-enriched Product of Alkali Melting Ti-bearing Blast Furnace Slag by Dilute Sulfuric Acid Leaching

The extraction of titanium from the Ti-enriched product which was prepared from Ti-bearing blast furnace slag by alkali roasting and water leaching, was investigated by dilute sulfuric acid leaching. The effects of sulfuric acid mass fraction, the ratio of acid to slag, reaction temperature and time on the extraction rate of titanium were studied in this paper. The results show that titanium recovery of 92.62 pct was obtained under the conditions of sulfuric acid mass fraction of 50 pct, ratio of acid to slag of 1.5:1, reaction temperature of 160°C and reaction time of 2.5hours. The kinetic study indicates that the acid leaching reaction was controlled by the rate of diffusion, and kinetics equation of drozdov can be described the acid leaching reaction.

The use of demineralisation and torrefaction to improve the properties of biomass intended as a feedstock for fast pyrolysis

Pre-treatments of biomass were investigated to reduce its undesirable properties which may affect the quality of fast pyrolysis bio-oil. A pre-treatment sequence was developed in this study to incorporate both biomass demineralisation and torrefaction. Demineralisation was performed by dilute acid leaching, primarily to reduce the inorganic concentration in raw biomass, whereas torrefaction targeted a reduction of the carboxyl, moisture and oxygen content. The liquid produced during torrefaction was recycled back as the leaching reagent for demineralisation. This solution contained dilute organic acids; therefore, the viability of leaching with organic acids (acetic and formic acid) compared to commonly used mineral acids (sulphuric, nitric and hydrochloric acid) was validated. Synthetic leaching solutions reduced the inorganic content in raw biomass from 0.41wt% to 0.14wt% when leached with 1% formic acid and to 0.16wt% when leached with 1% acetic acid, which was comparable to leaching with the mineral acids. Recycled torrefaction liquid that contained other acidic compounds in small quantities reduced the inorganic content to 0.14wt%, suggesting it is effective to use the recycled torrefaction liquid as the leaching solution. From the experimental results, the optimal conditions for biomass torrefaction were 260°C for 20min to minimise the char formation during pyrolysis, based on the increase in the acid-insoluble fraction of the biomass. However, the torrefaction temperature may be increased to 280°C if further reductions in acetyl and oxygen content are required. Higher temperatures are associated with severe biomass loss and the initiation of hydrogen loss. It should be noted that even at 280°C, the oxygen reduction is minimal. If oxygen reduction is the principal target when pre-treating biomass, it is suggested that torrefaction alone is not a suitable method to obtain bio-oil with a low oxygen content due to the low pyrolysis yields obtainable. This study demonstrated that the combined use of demineralisation and torrefaction as biomass pre-treatments has the ability to decrease the inorganic, acetyl and moisture content of biomass, which reduces undesirable catalytic reactions during fast pyrolysis to improve the quality of bio-oil produced.

Factors of Extracting Lithium from Lepidolite by Sulfate Roasting and Dilute Sulphuric Acid Leaching

Sulfate roasting and dilute sulphuric acid leaching were applied to extract lithium from lepidolite. Several conditions including roasting temperature, roasting time, K2SO4and CaO were investigated to improve the lithium extraction efficiency, the final lithium extraction efficiency could attain 94% with the conditions as follows: roasting temperature 850°C, roasting time 2 h, K2SO4to lepidolite mass ratio 0.15 and CaO to lepidolite mass ratio 0.75.

Multistage dilute acid leaching of a medium grade iron ore to super-concentrate

The phosphorous laden Koton Karfe iron ore is a medium grade iron ore deposit in Nigeria that can be upgraded as a super-concentrate for use at the Aladja Steel Midrex plant. The 75 μm size sample fraction of the ore was preconcentrated with shaking table and leached in the oven at atmospheric pressure with dilute hydrochloric acid in single and multistage leaching sequences of H2O-HCl-H2O and HCl-H2O-H2O. The as-received, as-tabled and asleached samples were then subjected to X-ray fluorescence and microscopic analyses. The results obtained showed that the H2O-HCl-H2O route produced a higher grade concentrate that assayed 68.54% Fe indicating about 58% upgrade in iron content; while the phosphorus and sulphur contents were reduced by about 77 and 99.6% respectively. In addition, the silicon, manganese, and titanium contents were drastically reduced, while potassium was completely eliminated. The upgrade of iron content in the ore to 68.54% and the drastic reduction in phosphorous and sulphur contents has thus rendered the Koton Karfe iron ore suitable for use as a super concentrate for the Aladja steel plant direct reduction iron making process.

Nickel recovery from spent Raneynickel catalyst through dilute sulfuric acid leaching and soda ash precipitation

Pharmaceutical industry makes extensive use of Raneynickel catalyst for various organic drug intermediates/end products. Spent catalysts contain environmentally critical and economically valuable metals. In the present study, a simple hydrometallurgical process using dilute sulfuric acid leaching was described for the recovery of nickel from spent Raneynickel catalyst. Recovery of nickel varied with acid concentration and time, whereas temperature had negligible effect. Increase of S/L ratio to 30% (w/v) showed marginal effect on nickel (90%) recovery, whereas Al recovery decreased drastically to ∼20%. Under the optimum conditions of leaching viz: 12 vol.% H 2SO 4, 30 °C, 20% solid to liquid (S/L) ratio and 120 min reaction time, it was possible to recover 98.6% Ni along with 39.2% Al. Leach liquor [pH 0.7] containing 85.0 g/L Ni and 3.25 g/L Al was adjusted to pH 5.4 with 30 wt.% alkali for quantitative aluminum removal. Nickel loss was about 2% during this Al removal step. Nickel from the purified leach liquor was recovered as nickel carbonate by adding required amount of Na 2CO 3. The purity of NiCO 3 product was found to be 100% with a Ni content of 48.6%. Na 2SO 4 was recovered as a by-product with a purity of 99%. Complete process is presented.

A comparison of an optimised sequential extraction procedure and dilute acid leaching of elements in anoxic sediments, including the effects of oxidation on sediment metal partitioning

The effect of oxidation of anoxic sediment upon the extraction of 13 elements (Cd, Sn, Sb, Pb, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, As) using the optimised Community Bureau of Reference of the European Commission (BCR) sequential extraction procedure and a dilute acid partial extraction procedure (4 h, 1 mol L −1 HCl) was investigated. Elements commonly associated with the sulfidic phase, Cd, Cu, Pb, Zn and Fe exhibited the most significant changes under the BCR sequential extraction procedure. Cd, Cu, Zn, and to a lesser extent Pb, were redistributed into the weak acid extractable fraction upon oxidation of the anoxic sediment and Fe was redistributed into the reducible fraction as expected, but an increase was also observed in the residual Fe. For the HCl partial extraction, sediments with moderate acid volatile sulfide (AVS) levels (1–100 μmol g −1) showed no significant difference in element partitioning following oxidation, whilst sediments containing high AVS levels (>100 μmol g −1) were significantly different with elevated concentrations of Cu and Sn noted in the partial extract following oxidation of the sediment. Comparison of the labile metals released using the BCR sequential extraction procedure (ΣSteps 1–3) to labile metals extracted using the dilute HCl partial extraction showed that no method was consistently more aggressive than the other, with the HCl partial extraction extracting more Sn and Sb from the anoxic sediment than the BCR procedure, whilst the BCR procedure extracted more Cr, Co, Cu and As than the HCl extraction.

The role of Ag [sbnd]O [sbnd]Al species in silver–alumina catalysts for the selective catalytic reduction of NO x with methane

We examined the role of silver and alumina in Ag–alumina catalysts for the selective catalytic reduction (SCR) of NO x by methane in gas streams containing excess oxygen. A cogelation technique was used to prepare Ag–alumina materials with high dispersion of silver even at high metal loadings (>10 wt%) and after air calcination at 650 °C. Typically, a part of silver is present as fine nanoparticles on the alumina, whereas another part is ionic, bound with the alumina as [Ag O Al] species. Dilute nitric acid leaching was used to remove the silver particles and all weakly bound silver from the surface of these materials. Complementary structural characterization was performed by HRTEM, XPS, XRD, and UV–vis DRS. We found that the higher the initial silver content, the higher the amount of the residual [Ag O Al] species after leaching. NO–O 2-TPD tests identified that silver does not modify the surface properties of the alumina. The SCR reaction-relevant NO x adsorption takes place on alumina. Temperature-programmed surface reaction (TPSR) and kinetic measurements at steady state were used to check the reactivity of the adsorbed NO x species with methane and oxygen to form dinitrogen. Only the alumina-adsorbed nitrates react with CH 4 to produce N 2 in the presence of oxygen, beginning at ∼300 °C as found by TPSR. Moreover, the SCR reaction rates and apparent activation energies are the same for the leached and parent Ag–alumina catalysts. Thus, metallic silver nanoparticles are spectator species in CH 4-SCR of NO x . These catalyze the direct oxidation of methane at temperatures as low as 300 °C, which explains the lower methane selectivity for the SCR reaction measured over the parent samples.

Effectiveness of leaded petrol phase-out in Tianjin, China based on the aerosol lead concentration and isotope abundance ratio

The phase-out of leaded petrol has been a measure widely used to reduce atmospheric lead pollution. Since the 1980s, China began to promote unleaded petrol. In order to assess the effectiveness of the measure an isotope fingerprint technique was applied for aerosol samples in the city of Tianjin. After dilute acid leaching, the lead concentration and isotope abundance ratios were determined for 123 samples collected in Tianjin during eight years (1994–2001). The 206Pb / 207Pb ratio was lower in summer, when coal combustion emission was low and vehicle exhaust became more important, indicating that the 206Pb / 207Pb ratio of leaded petrol in Tianjin is lower than that of aerosol samples. The 206Pb / 207Pb ratio gradually increased from 1994 to 2001, a trend that suggests that the contribution from vehicle exhaust was diminishing. Overall, the measurements matched well with national statistical data of leaded and unleaded petrol production. After the nationwide switch to unleaded gasoline, comprehensive control measures are urgently needed to reduce air lead pollution in China, as aerosol lead reduced slightly but remains at a relatively high level.

Saturated hydraulic conductivity of a volcanic ash soil affected by repulsive potential energy in a multivalent anionic system

Acid rain is supposed to influence soil structures, because soils have pH-dependent charges. The adverse effects of acid rain on soils must be assessed. Although repulsive potential energy among soil clay particles generates swelling and dispersion, thereby changing the soil’s hydraulic conductivity, the relationship between hydraulic conductivity and repulsive potential energy has not been evaluated. Moreover, research into repulsive potential energy in multivalent counterionic systems has been rare. In this paper, repulsive potential energies for a volcanic ash soil (allophanic Andisol), which is characterized by a number of pH-dependent charges, were evaluated in a multivalent counterionic system. Changes in saturated hydraulic conductivity (K) of volcanic ash soil during dilute acid leaching and their relationship with the repulsive potential energies were examined. When nitric acid at pH 3 or 4 was leached, K decreased rapidly. On the other hand, the decrease in K attenuated as the proportion of sulfate in the dilute acid increased. Electrophoretic mobilities were measured and the zeta potentials were estimated. From the zeta potentials and the calculation of repulsive potential energies between the clay particles in the NO3–SO4 system, we concluded that the decrease in K for an acid solution with a high proportion of nitrate was due to swelling and dispersion of the soil induced by electrostatic repulsive potential energy. Because sulfate formed complexes on the clay surface, the repulsive potential energy decreased as the proportion of sulfate in the dilute acid increased. Then, the flocculation of the soil was maintained, thereby inhibiting the decrease in K.

Enrichment adsorption of a labile substance to the surface of particular mineral particles in river water as investigated by SEM-EDX and dilute-acid extraction/ICP-MS.

The selective enrichment behavior of a labile substance, such as hydroxides, to the surface of particular mineral particles in river water was clarified by scanning electron microscopy/energy dispersive X-ray microanalysis (SEM-EDX). Individual particles other than diatom collected on a 0.45 microm filter from the Fuji and Sagami rivers, central Japan, were analyzed by SEM-EDX and classified into seventeen groups according to the chemical composition and shape. Phosphorus, sulfur, chlorine, manganese and copper detected in each particle collected on the 0.45 microm filter could be successfully used as effective indicators of labile substance secondarily formed and adsorbed afresh in river water, because the detection frequencies of such elements are quite low, or negligible, in fresh mineral particles derived from igneous rocks. The labile substance adsorbed on mineral particles collected on the 0.45 microm filter was also evaluated by dilute-acid leaching, followed by inductively coupled plasma mass spectrometry (ICP-MS). Almost all parts of the manganese detected in individual particles were those adsorbed afresh as hydroxides together with iron and aluminum. Also, anionic elements, such as phosphorus, sulfur and chlorine, formed complexes with the hydroxides and/or were incorporated in them. Mg and/or Ca-rich aluminosilicate groups were the most effective adsorbers of such labile species. However, Si-rich and Na-, K- and Na-Ca rich aluminosilicates did not significantly adsorb the labile substance. Consequently, the remarkable selectivity was clarified in the adsorption process of labile substance to individual mineral particles in river water.

Comprehensive processing of low grade sulphidic molybdenum ores

Low-grade sulphidic molybdenum ores were treated by using a combined processing route for a comprehensive recovery of molybdenum, copper, and other minor elements. As the first step, oxidation roasting was used to convert most of sulphides into metal oxides, during which 85–90% of sulphur was removed. Then both water and dilute sulphuric acid leaching of the roast were tested, in order to remove silica, iron and other impurities from the roast. Both copper and molybdenum were recovered one after another from the filtrates via cementation by iron powder under controlled temperature and pH conditions. Recovery for both elements was in all cases over 99%. Reasonable separation efficiency for copper and molybdenum was achieved from the water leach solutions. The leached cakes were dissolved in ammonia to recover the molybdenum by crystallisation as ammonium-dimolybdate. The proposed roasting, leaching and separation steps give a feasible alternative for a comprehensive processing of low grade molybdenum ores.

Comparison between non-residual Al, Co, Cu, Fe, Mn, Ni, Pb and Zn released by a three-step sequential extraction procedure and a dilute hydrochloric acid leach for soil and road deposited sediment

Surprisingly little is known about the relationship between the labile phases removed by sequential extraction procedures and those liberated by single leaches that minimally impact the alumino-silicate matrix of solids. This investigation examines the relationship between the summed concentrations of Al, Co, Cu, Fe, Mn, Ni, Pb and Zn released by an optimized 3-step standardized sequential extraction procedure and those released by a single 0.5 M HCl leach. Thirty-nine representative soil and road deposited sediment samples were examined from an urban watershed, in Honolulu, Hawaii, which has been shown to have a high degree of traffic-associated pollution. Properties of samples analyzed varied widely and exhibited a range in cation exchange capacities from 7 to 59 cmol c/kg, pH values from 3.5 to 7.9, and organic C contents from 1 to 29%. Results indicate that the dilute HCl leach was slightly more aggressive than the sequential procedure as it removed significantly more Al, Cu, Fe, Mn and Ni; though no significant differences were observed between Co, Pb and Zn concentrations liberated by the two approaches. Both approaches showed limited dissolution of the crystal lattice with ⩽9% of the total Al liberated. Regardless of approach, element mobility was the same with the order being: Pb>Mn>Zn>Co≈Cu>Ni>Fe ∼ Al. Regression analysis indicated highly significant ( P<0.0001) logarithmic relationships between the two digestion procedures, with coefficients of determination ( r 2) ⩾92% for all elements except Fe (54%) and Ni (64%). Further support for the strong relationships between elements liberated by both digestions was gained from geochemical contrasts between anomalous and background levels and concentration enrichment ratios. This was particularly true for Pb and Zn, the most anthropogenically enhanced trace metals in the watershed. All data indicated that a dilute HCl leach was a valuable, rapid, and cost-effective analytical tool in contamination assessment.

Lead analysis of sediment cores from seven Connecticut lakes

Lead analyses were performed on sediment cores from seven Connecticut lakes by dilute acid leaching. The absolute concentrations of lead varied from core to core, but the lead profiles were similar in all of the cores, and each depicted a point where the concentration of lead sharply increased above background levels. The background lead concentrations observed in the bottom portions of the cores ranged from 12-54 μg Pb/g sediment with a mean of 30 μg Pb/g, and increased to a mean maximum of 310 μg Pb/g. In six of the lakes significant increases above background levels were not noted until between 1924 and 1952, suggesting that, at least for Connecticut lakes, the point in a lake sediment core where the concentration of lead began to increase was after ca. 1924, and on average about 1930. Lead concentrations declined in the surface sediments of only three of the lakes, mostly since the 1980's, and presumably in response to the phasing out of leaded gasoline. However, significant declines in lead concentrations were not observed in the remaining cores, possibly due to increased motor vehicle use within the airshed of the lakes and/or changes in the export of lead to the lakes from their watersheds.

Hydraulic Conductivity of an Allophanic Andisol Leached with Dilute Acid Solutions

When the soil contains a substantial amount of pH‐dependent charges, pH strongly influences hydraulic conductivity. Adverse effects of acid rain and chemicals on soils have been observed, but few studies have focused on hydraulic conductivity change due to pH. Changes to the saturated hydraulic conductivity (K) of allophanic andisol (volcanic ash soil), which has a substantial amount of pH‐dependent charges, during dilute acid leaching were examined in this study. K was determined at a constant hydraulic gradient in soil columns. Influent solutions of HNO3 and H2SO4 were prepared at pH 3 and 4. Tensiometer pressure potential and pH distribution in the soil columns were measured. Clay dispersion was measured by optical transmission and soil buffer capacity was evaluated from acid titration curves. K decreased during HNO3 leaching but increased during H2SO4 leaching. Because of the high buffer capacity of the soil, the influence of acid leaching on the soil structure was significant only at the soil surface. Soil dispersion was observed only in HNO3 solution. No dispersion was observed in H2SO4 solution because of the strong specific adsorption of SO2−4 The swelling and dispersion of the soil at the surface layer caused the decrease in K during HNO3 leaching, while these processes were prevented in H2SO4 leaching.

Ordovician radiolaria from bedded cherts of the Southern Uplands

Synopsis Dilute hydrofluoric acid leaching of radiolarian cherts has yielded the first identifiable radiolaria from the Northern Belt of the Southern Uplands. The radiolaria are abundant, as are sponge spicules, and occur with spindle-shape hollow biomorphs of unknown affinity. The red-brown chert sequence at Hawkwood Burn may be correlated with the upper Llanvirn (Llandeilian)–Caradoc Haplentactinia juncta – Inanigutta unica assemblage in Nazarov’s (1988) biozonation. The presence of Protoceratoiciskum sp. and the absence of typical Arenig morphotypes indicates that the greenish-grey cherts near Crawford can also be tentatively regarded as of Llanvirn-Caradoc age ( sensu Fortey et al. 1995 ).

コバルトクラスト酸性浸出液中に存在する有価金属の抽出と分離

Cobalt crust, one of the mineral resources at the seabed, includes nickel, cobalt, copper, iron and manganese fairly.At the beginning of this study, the dilute sulfuric acid leaching have been occurred on cobalt crust using hydrogen peroxide as a reductant. As a result of the leaching test, almost of all valuable metals in the cobalt crust were leached in the solution.By addition of the calcium carbonate in the leaching solution, iron was removed completely as iron hydroxide. In this time, the other valuable metals were not effected by the calcium carbonate.In the experiment of extraction, 10% LIX-84I kerosene solution was used. The extraction percentage from the leached solution with the 10% LIX 84-I kerosene solution were more than 99% for nickel, cobalt at pH: nearly 7.0 and copper at pH: nearly 2.0.In the stage of extraction, the separation of nickel and cobalt was difficult, because of the same extraction behavior. Therefore, the studies were occurred on separation by stripping. In the stripping from the organic phase containing nickel, cobalt and copper, copper was stripped with the hydrochloric acid solution at pH: nearly O. Nickel was stripped at pH: 1. After this operation, cobalt may be got by hydrogen sulfide.

Alcohol-modified hydrochloric acid leaching of sea nodules

The effects of propanol and butanol additions in dilute hydrochloric acid leaching of Cu, Fe, Mn, Ni and Co from sea nodules from the Indian Ocean were investigated. In the absence of any additive, dilute hydrochloric acid (2.75 M) in aqueous medium leaches only 80% copper and 60% iron. More than 90% recovery of all the metals is achieved only when highly concentrated acid (11 M) is used. It has been found that metal recoveries can be considerably improved even in 2.75 M HCl solution if an appropriate amount of propanol or butanol is incorporated. Addition of only 9 vol% propanol or 4.5 vol% butanol is sufficient for achieving about 90% recovery of each of the metals. It has been further observed that the amount of alcohol required for the satisfactory recovery of metals decreases with the use of longer chain length alcohols. The effects of other parameters, such as the period of leaching and acid concentration, on the recovery of metals was also studied.

Lead isotope systematics of granitoid weathering

The isotopic composition of lead released by chemical weathering of granitoids was investigated in order to evaluate the sensitivity of this natural tracer as a tool for monitoring mineral weathering and soil development. The isotopic composition of lead was found to change systematically with the relative degree (or maturity) of weathering in both Cretaceous granitoids from the Sierra Nevada batholith (SN) and Precambrian granitoids from the Wind River Range, Wyoming (WRR). In the SN, lead released from crushed bedrock by dilute acid leaching (to simulate the initial stages of weathering) has a composition more radiogenic than observed in soils (average 206Pb 207Pb = 1.335 ). Lead released by leaching from soils developed on a relatively young terrain (~10 kyr old) is less radiogenic (average 206Pb 207Pb = 1.270 ) than crushed bedrock and lead released by leaching from soil developed on older surfaces (~ 100 kyr) is even less radiogenic (average 206Pb 207Pb = 1.255 ). Lead released from the total digestion of the rock has the least radiogenic composition (average 206Pb 207Pb = 1.240 ). In the WRR, systematic changes in the isotopic composition of lead released by leaching were observed in soils developed on glacial moraines of variable ages. Lead released from soil developed on a 21 kyr old moraine was the most radiogenic ( 208Pb 207Pb = 3.257 ). Lead released from soil developed on a 130 kyr old moraine was less radiogenic ( 208Pb 207Pb = 2.780 ) and lead released from soil developed on ≥350 kyr old moraine was the least radiogenic ( 208Pb 207Pb = 2.532 ). The observed systematic changes in the isotopic composition of lead with time in both field areas demonstrates the potential of lead isotopes to ascertain the degree (or maturity) of chemical weathering of granitoids and may have applications in determinations of the relative ages of some glacial deposits.

Preliminary studies of the CHIM electrogeochemical method at the Kokomo Mine, Russell Gulch, Colorado

Abstract The CHIM electrogeochemical exploration technique was developed in the former Soviet Union about 20 years ago and is claimed to be effective in exploration for concealed mineral deposits that are not detectable by other geochemical or geophysical techniques. The method involves providing a high-voltage direct current to an anode and an array of special collector cathodes. Cations mobile in the electric field are collected at the cathodes and their concentrations determined. The U.S. Geological Survey started a study of the CHIM method by conducting tests over a precious- and base-metal-bearing quartz vein covered with 3 m of colluvial soil and weathered bedrock near the Kokomo Mine, Colorado. The tests show that the CHIM method gives better definition of the vein than conventional soil geochemistry based on a total-dissolution technique. The CHIM technique gives reproducible geochemical anomaly patterns, but the absolute concentrations depend on local site variability as well as temporal variations. Weak partial dissolutions of soils at the Kokomo Mine by an enzyme leach, a dilute acetic acid leach, and a dilute hydrochloric acid leach show results comparable to those from the CHIM method. This supports the idea that the CHIM technique is essentially a weak in-situ partial extraction involving only ions able to move in a weak electric field.