Coprecipitation Phenomena Research Articles

γʹ and γ″ co-precipitation phenomena in directly aged Alloy 718 with high δ-phase fractions

Co-precipitation of γ′ and γ′′ is the main strengthening mechanism that provides superior high-temperature strength in directly aged Alloy 718 aerospace parts. Control of their morphology, fraction, and configuration might allow exposure to more demanding operation environments in next-generation aircraft engines. The density of geometrically necessary dislocations introduced during hot deformation has been shown to significantly affect the co-precipitate morphology of γ′ and γ′′ in materials free of the δ-phase. However, the combined effects of geometrically necessary dislocation density and lower Nb content due to higher δ-phase fractions on co-precipitation behaviour and strengthening remain unknown. We verify these effects by hardness testing as a proxy for high-temperature strength in materials with 4.1 % δ-phase fraction. Deformation at 950 °C yields a remarkable increase of 12 % in hardness after direct ageing, explained by the prevalence of complex co-precipitate configurations. Deformation at 1000 °C decreases the δ-phase fraction and geometrically necessary dislocation density but achieves up to 19 % volume fractions of γ″, leading to a predominance of monoliths and duplet co-precipitates and a better direct ageing response. Atom probe microscopy reveals the flux of elements during co-precipitation. We recommend a δ-annealing treatment before the final forging step for manufacturing stronger Alloy 718 aerospace parts.

Using multivariate compositional data analysis (CoDA) and clustering to establish geochemical backgrounds in stream sediments of an onshore oil deposits area. The Agri River basin (Italy) case study

Establishing the natural background levels of chemical elements is very often extremely complicated. This is even more true especially for the more anthropized areas, where the concentration of an element in the environmental matrices is conditioned not only by the natural (geogenic) context but also by anthropic activities. In this study, the natural background levels (NBLs) of several chemical elements in the stream sediments of the High Agri River basin have been calculated using a combination of multivariate statistical analysis (MSA) and machine learning techniques in the frame of compositional data analysis (CoDA). Specifically, data clustering and robust principal component analysis (rPCA) have allowed us to recognize and isolate three different data populations, belonging to three different geological domains. A first population of data is clearly related to calcareous lithologies, while the second one is associated to siliciclastic lithologies. A third one is of mixed origin, partly linked to the volcanoclastic nature of the sediments and due to the presence of co-precipitation phenomena. The three data populations have been later separated into three different databases and, whereas needed, the outliers have been eliminated. Based on the obtained results, the NBLs have been calculated using the US-EPA's (United States Environmental Protection Agency) ProUCL software. The results derived from this new approach have been later compared with those obtained using the spectral analysis (S-A) method to evaluate its advantages and versatility. This approach allowed calculating more reliable natural background values.

Kinetic and isothermal sorption of antimony oxyanions onto iron hydroxide during water treatment by coagulation process

Antimony (Sb) is a regulated pollutant that is frequently present at elevated concentrations in natural bodies of water due to natural sources and human activities. Therefore, its purification from fresh water streams is of ultimate importance. This study focused on the iron hydroxide (FHO) formation and removal of Sb ions from water via ferric chloride (FC) coagulation. The effects of pH, contact time, concentration, temperature, and ionic strength (IS) were studied to explore the mechanistic insights into the removal behavior of both Sb ions during potable water purification. Results indicated that the solubility of FHO decrease by increasing the pH, thus repulsing the oxyanions at alkaline pH, decreasing in turn the adsorption capacity of Sb(V) species. The influence of contact time and equilibrium Sb concentration on FHO formation was found to be insignificant. The adsorption of Sb on FHO was well fitted with Pseudo-first order and Langmuir-Freundlich (L–F) models. Physical adsorption of Sb ions onto FHO was identified to be the major mechanism using the Dubinin-Radushkevich (D–R) isotherm model. Thermodynamic parameters (ΔG, ΔH, and ΔS) suggested that the Sb adsorption process was spontaneously exothermic with increased randomness. A more pronounced effect of IS on high Sb feed was observed with increasing sorption affinities upon enhancing electrolyte concentration. The mechanism was further supported by X-ray diffraction spectroscopy, which revealed the likelihood of inner-sphere complexation and physisorption of Sb onto FHO. Moreover, an involvement of coprecipitation phenomena during growing FHO was observed as key phenomena for greater Sb(III) removal. In general, the results of current research may provide detailed insights into the adsorption ability of FHO and the potential mechanisms responsible for the removal of Sb ions during potable water treatment.

Mechanism of arsenate coprecipitation at the solid/liquid interface of ferrihydrite: A perspective review

Arsenate (As(V)) is a toxic element in acid mine drainage and has to be removed during the neutralization process. Coprecipitation with ferrihydrite is the main mechanism for As(V) removal from acid mine drainage. To improve treatment efficiency, a quantitative understanding of the coprecipitation mechanism is required. Coprecipitation can incorporate more As(V) into ferrihydrite than adsorption. The results of XRD (X-ray Diffraction) and XANES (X-ray Adsorption Near Edge Structure) analysis confirmed that the formation of poorly crystalline ferric arsenate increased when the initial As/Fe molar ratio increased in the coprecipitation with ferrihydrite. EXAFS (Extended X-ray Adsorption Fine Structure) analysis at the iron K-edge showed that the proportion of octahedral structures in ferrihydrite increased when the initial As/Fe molar ratio increased. Moreover, EXAFS analysis at the arsenic K-edge, assuming three kinds of surface complexes for the AsFe bond, revealed that the coordination number for AsFe with an atomic distance of 2.85 × 10−10 m increased and that for As-Fe with an atomic distance of 3.24 × 10−10 m decreased as the initial As/Fe molar ratio increased. Thus, for more efficient wastewater treatment, active control of coprecipitation phenomena according to mechanistic details is essential.

Difunctional chitosan-stabilized Fe/Cu bimetallic nanoparticles for removal of hexavalent chromium wastewater

Bimetallic Fe/Cu nanoparticles were successfully stabilized by chitosan used for remediating hexavatlent chromium contaminated wasterwater. However, the over-loaded chitosan on the surface of Fe/Cu particles limited the Cr(VI) reduction due to the occupation of the surface reactive sites. Weighing the colloid stability and the reduction reactivity, the optimal dosage of chitosan is 2.0 wt% and the optimal Cu doping dosage is 3.0 wt%. SEM and TEM images showed that the chitosan-stabilized Fe/Cu bimetallic nanoparticles (CS-Fe/Cu nanoparticles) were uniformly dispersed, which had loose and porous surface. FTIR characterization showed that the binding sites of nZVI and chitosan. XRD demonstrated that the presence of copper and chitosan did not change the existence form of zero-valent iron. Most importantly, the contribution of chitosan and Cu in the removal mechanism was studied by the reduction experiments and the XPS analysis. On the one hand, chitosan could effectively combine with Cr(VI) due to chelation, on the other hand, Cu played an important role in the precipitation and coprecipitation phenomena. These findings indicate that CS-Fe/Cu has the potential to be a promising material for wastewater treatment.

Deproteinization assessment using isotopically enriched compounds to trace the coprecipitation of low-molecular-weight selenium species with proteins

Studies have shown that information related to the presence of low-molecular-weight metabolites is frequently lost after deproteinization of complex matrices, such as blood and plasma, during sample preparation. Therefore, the effect of several deproteinization reagents on low-molecular-weight selenium species has been compared by species-specific isotope labeling. Two isotopically enriched selenium tracers were used to mimic models of small inorganic anionic (77Se-selenite) and organic zwitterionic (76Se-selenomethionine) species. The results presented here show that the use of a methanol-acetonitrile-acetone (1:1:1 v/v/v) mixture provided approximately two times less tracer loss from plasma samples in comparison with the classic procedure using acetonitrile, which may not be optimal as it leads to important losses of low-molecular-weight selenium species. In addition, the possible interactions between selenium tracers and proteins were investigated, revealing that both coprecipitation phenomena and association with proteins were potentially responsible for selenite tracer losses during protein precipitation in blood samples. However, coprecipitation phenomena were found to be fully responsible for losses of both tracers observed in plasma samples and of the selenomethionine tracer in blood samples. This successfully applied strategy is anticipated to be useful for more extensive future studies in selenometabolomics.

Local autocatalytic co-precipitation phenomena in self-assembled silica–carbonate materials

Under certain conditions, precipitation of barium carbonate in alkaline silica-rich environments affords unusual polycrystalline aggregates exhibiting curved shapes and hierarchical structuring, very much reminiscent of biogenic mineral tissues. The formation of these so-called silica biomorphs is thought to rely on a coupling of chemical equilibria in solution, which drives concerted co-mineralization and self-assembly of components. In the present work, we have studied the effect of fluid motion on morphogenesis by conducting syntheses in media stirred at different rates and exposed to an ultrasonic field, respectively. The traced growth behavior is discussed on the basis of statistical analyses of the occurring morphologies as well as in terms of expected changes in the supersaturation of the system. It is shown that the observed complex architectures arise as a consequence of an autocatalytic precipitation cycle, during which evolving aggregates synthesize and organize their constituents on their own upon growth. These processes occur only at a local scale within a certain active region that appears to extend over some microns beyond the growth front. Our findings provide concrete experimental evidence supporting the proposed formation mechanism and suggest that growth of silica biomorphs is independent of mass transport from the bulk, unless forced convection becomes strong enough to affect the active region and hence interfere with autocatalysis.

Arsenic from Groundwater to Paddy Fields in Bangladesh: Solid–Liquid Partition, Sorption and Mobility

The arsenic contamination of Bangladesh groundwater involves heavy arsenic inputs to irrigated rice fields. Beside adsorption on soil colloids, iron–arsenic co-precipitation phenomena can affect arsenic retention in soils. In paddy fields of Satkhira District, Bangladesh, the study of the arsenic and iron forms in the irrigation waters and in soils at different times and distances from the irrigation well evidenced that a higher Fe/As ratio in the well water was related to a faster oxidation of Fe(II) and As(III) in water and to a close Fe–As association in soils, together with a greater accumulation of arsenic and poorly ordered iron oxides. The concentration of arsenic and of labile iron forms decreased with the distance from the well and with the depth, as well as the reversibility of arsenic binding. The fate of the arsenic added to the soils by irrigation hence resulted strongly influenced by iron–arsenic co-precipitation, depending on the Fe/As ratio in water. Irrigation systems favouring the sedimentation of the Fe–As flocks could help in protecting the rice from the adverse effects of dissolved arsenic.

A Quantitative Modeling of Co-precipitation Phenomena in Wastewater Containing Dilute Anions with Ferrihydrite using a Surface Complexation Model

Although numerous qualitative studies have been published on removal characteristics from wastewater of dilute anions by co-precipitation treatment with Fe(III) or Al salts, detailed mechanisms or quantitative characteristics are not well understood. In this study, a quantitative modeling of co-precipitation phenomena in wastewater containing dilute As(V), Se(VI), Cr(VI) or F with ferrihydrite was tried using a diffuse layer model (DLM), which is one of the most popular and simplest of surface complexation models. Co-precipitation experimental results from wastewater containing 2 mg/dm3 of Se(VI), 2 mg/dm3 of Cr(VI), or 15 mg/dm3 of F with ferrihydrite could be predicted quantitatively by the DLM with a existing set of parameters. However, results from wastewater containing 10 mg/dm3 of As(V) with ferrihydrite could not be predicted quantitatively but only qualitatively by the model. It was confirmed from the comparison of co-precipitation experimental results and simple adsorption ones that this quantitative difference between experimental and calculation data resulted from the procedure difference between co-precipitation and simple adsorption; in short, the precipitation of ferrihydrite and adsorption of As(V) develop simultaneously in the former system, and only As(V) adsorbs onto prepared ferrihydrite in the latter system.

Coprecipitation of thorium and lanthanum with UO2+x(s) as host phase

Coprecipitation may be a significant process in controlling radionuclide release during spent fuel dissolution/reprecipitation in a breached geological disposal site by water. The objective of this work was to study the coprecipitation of thorium and lanthanum with UO2+x(s) as host phase under reducing conditions (pure N2andEh=−300 mV/SHE) as a function of pH and [Th]/[U+Th] or [La]/[U+La] initial concentration ratios. At pH values between 3 to 9, the final concentrations of dissolved Th and La were found to be considerably lower than expected if pure phases, Th(OH)4(s) and La(OH)3(s) would have been formed. Coprecipitation phenomena and formation of solid solutions ThyU1-yO2+x′(s) and (U,La)O2+x′(s) are suggested to be responsible for the lower solubility.

水酸化鉄化合物を用いた廃水中に含まれるヒ素の吸着除去

The treatment of wastewater contaminated by arsenic (As) ion is an important issue as a lot of abandoned mines in Japan. Normally, the co-precipitation process with ferric/ferrous ions by neutralization is used to remove arsenic ion from mines wastewater by using CaCO3, Ca(OH)2, NaOH etc. However, the process has some problems: It needs a lot of alkali reagents and produces a lot of the neutralized sludge. Therefore, in this research the synthesis of iron hydroxide compound as absorbent for arsenic ion was developed in our laboratory. The adsorptive properties of the arsenic ion in artificial wastewater (incl. As and SO42-) and practical mine wastewater from abandoned mine were investigated by using the iron hydroxide compound. The results are as follows:(1) The iron hydroxide compound has a high adsorption capacity for the wastewater containing arsenic ion with pH 4 to 6. In case of practical mine wastewater, it could remove the arsenic ion under Japanese standard regulations (0.1 mg/l) even if 1 gram per liter adsorbent was added in the wastewater at pH 4. It indicated that the iron hydroxide compound could achieve high removal performance of arsenic in mine wastewater not only co-precipitation phenomena.(2) The maximum arsenic ion adsorption capacity of iron hydroxide compound was 87.32 mg per gram. In addition, it was observed the arsenic is adsorbed on the surface of iron hydroxide compound. Moreover, the CaCO3 has a feasibility to use as an alkali reagent, as it could remove the arsenic ion from practical mines wastewater, similar with NaOH.

Fenton’s pre-treatment of mature landfill leachate

The aim of this study was to check the effectiveness of the Fenton’s reagent (Fe 2+ + H 2O 2 + H +) for the pre-treatment of a municipal landfill leachate with the objective of improving its overall biodegradability, evaluated in terms of BOD 5/COD ratio, up to a value compatible with biological treatment. The leachate came from a municipal sanitary landfill located in southern Italy and the average values of its main parameters were: pH=8.2; COD=10 540 mg l −1; BOD 5=2300 mg l −1; TOC=3900 mg l −1; NH 4-N=5210 mg l −1; conductivity=45350 μS cm −1; alkalinity=21 470 mg l −1 CaCO 3. The effect of initial pH value on the pre-treatment effectiveness was evaluated by titrating the amount of acidic by-products formed. The extent of leachate oxidation was monitored and controlled by both pH and redox potential measurements. The best operational conditions for achieving the desired goal (i.e., BOD 5/COD ⩾ 0.5) resulted: Fe 2+=275 mg l −1; H 2O 2=3300 mg l −1; initial pH=3; reaction time=2 h. At the end of the Fenton’s pre-treatment, in order to permit a subsequent biological treatment, residual ferric ions were removed increasing the pH up to 8.5 by adding 3 g l −1 of Ca(OH) 2 and 3 mg l −1 of a cationic polyelectrolyte, the latter as an aid to coagulation. This final step also resulted in a further modest removal of residual COD due to co-precipitation phenomena.

Coprecipitation of thorium with UO2

Summary Coprecipitation may be a significant process in controlling radionuclide (RN) release during spent fuel dissolution/reprecipitation in a breached geological disposal site by water. The objective of this work was to study the coprecipitation of thorium with UO2 as host phase under reducing conditions (pure N2 and E h<-100 mV/SHE) as a function of pH and [Th]/[U] initial concentration ratio. For pH < 4, the final concentration of Th was found to be considerably lower than expected if pure phase, Th(OH)4(s) was formed. Coprecipitation phenomena and formation of solid solutions (U,Th)O2+x(s) are suggested to be responsible for the lower solubility concentrations. For pH > 4, the final concentrations seems to be similar to pure phase solubility.

Coprecipitation phenomena during spent fuel dissolution. Part 1: Experimental procedure and initial results on trivalent ion behaviour

Coprecipitation may be a significant process in controlling radionuclide release during spent fuel dissolution in geological disposal. The coprecipitation behaviour of the trivalent elements Am, Cm and Eu with Na-polyuranates is studied in saline solutions. Experimental data are obtained by precipitation from a supersaturated solution of dissolved high burnup spent fuel in 5 m NaCl solution at pH values between 5.7 to 12. The resulting concentrations of dissolved Am, Cm and Eu were found similar to those observed in spent fuel leaching experiments and were found to be considerably lower than expected, if the formation of pure Am(OH) 3, Cm(OH) 3 and Eu(OH) 3 solid phases is assumed. Coprecipitation phenomena and formation of solid solutions are suggested to be responsible for the lower solubility concentrations.

X-ray absorption spectroscopic study of the sorption of Cr(III) at the oxide-water interface: II. Adsorption, coprecipitation, and surface precipitation on hydrous ferric oxide

The sorption of Cr(III) by hydrous Fe oxides involves adsorption, surface precipitation, and coprecipitation phenomena. These phenomena lead to different phases which are here compared with regard to both their Cr solubility and their local structure. The former is simulated by the “surface precipitation model” and the latter is derived from X-ray absorption fine-structure (EXAFS) spectroscopic data interpreted by the “polyhedral approach method.” The adsorption of a Cr(III) atom onto goethite or hydrous ferric oxide (HFO) occurs via the formation of inner-sphere surface complexes. In such complexes, Cr atoms are never isolated, but present as small surface hydroxy polymers. This polymerization has been catalyzed by the surface, and it occurs when Cr(III) bonds only 10% of the surface “active” sites (i.e., when it covers 1% of the BET surface area). In these surface polymers, Cr(III) atoms are surrounded by three metal (Fe or Cr) shells at 3.00–3.05, 3.40–3.46, and 3.94–4.03 Å, as in a mixed α- and γ-MeOOH local structure (Me = Fe or Cr). These polymers act as nuclei for the precipitation of a surface hydrous Cr oxide, a precipitation that starts under conditions undersaturated with respect to the homogeneous precipitation of the same oxide, a phenomenon well described by the surface precipitation model. This surface precipitate and the pure hydrous chromium oxide have identical solubility products and the same local structure (γ-CrOOH). On the contrary, when Cr(III) is coprecipitated with Fe(III), only two cation shells are detected around Cr(III) at 2.99 and 3.40 Å, indicating that Cr substitutes for Fe in an α-(Fe, Cr)OOH framework. A difference in local structure (α-CrOOH versus γ-CrOOH) therefore accounts for the difference in solubility products of the surface-precipitated and coprecipitated Cr hydroxides.

Chemical Composition of Ochreous Precipitates from Ohio Coal Mine Drainage

AbstractOchreous precipitates and associated solutions were collected from waters draining abandoned coal works at 28 locations in eastern Ohio. Major and trace element contents of the precipitates were determined, and comparisons were made with source solutions to evaluate the effects of pH, organic C, and ionic strength on solid‐phase composition and trace metal distribution. The pH and calcalated ionic strength of the effluents ranged from 2.6 to 7.8 and 6 to 106 mmol L−1, respectively. Associated precipitates consisted primarily of poorly crystallized oxides and oxyhydroxides of Fe with jarosite occuring as a major constituent of only one specimen. Mean Fe, SO4, Al, and Si contents of the precipitates were 8.7, 1.34, 1.11, and 0.25 tool kg−1, respectively. Silicon content increased with increasing pH of the source solution suggesting pH‐dependent adsorption. In contrast, SO4 and Al appeared to be influenced both by precipitation and adsorption reactions. Partition coefficients for As, B, Ba, Co, Cu, Cr, Mn, P, and Zn showed a preferential accumulation of all elements by the solid phase with mean log Kd values ranging from 2.9 for Cu to 6.3 for As. Manganese, Co, and Zn all showed increased partitioning into the solid phase with increasing pH and decreasing ionic strength of the drainage waters. Copper appeared to be strongly associated with organic matter, and a weaker but positive relationship was also observed with Co and Zn. No effects of pH, ionic strength, or organic C were observed for any other trace elements. Solubility equilibrium calculations suggested that the solid phase concentrations of Co, Cr, Cu, Mn, Zn, and As were primarily controlled by adsorption and/or coprecipitation phenomena whereas Ba and P activities in solution exceeded the solubilities of barite and strengite, respectively.

Simultaneous potentiometric micro-scale determination of chlorine and bromine in organic compounds

The experimental conditions for the micro-scale argentimetric potentiometric titration of organic chlorides and bromides present in the same solution were investigated. Coprecipitation phenomena affect the titration but can be minimised by various means, thus making it possible to determine both halogens with an absolute error of less than 0.40%. For the mineralisation of organic compounds containing halogens a Schoniger flask, modified in order to allow an exact titration of small solution volumes, was used. The titrations were performed with an automatic apparatus.

Radiochemical Techniques Applied to Laboratory Studies of Water Leaching of Heavy Metals from Coal Fly Ash

Assessment of the potential environmental impact of heavy metals (HM) mobilized by coal-fired power plants showed that water leaching of HM from pulverized fuel ash may for certain HM constitute an important pathway to the aquatic environment. This process was therefore investigated in more detail by laboratory experiments. Batch experiments were performed in order to simulate ash pond conditions, whereas column experiments were carried out to represent water leaching from fly ash deposits. Using highly sensitive radiochemical techniques such as radioactive tracers and neutron activation of fly ash the fate of a single HM could be easily followed even in very low concentration experiments. Employing radioisotopic tracers the distribution coefficients of simple ionic forms of As, Sb, Bi, Se, Te, Cr, Mo, W, Ni, Cd in a coal fly ash/water system could be determined as a function of pH. Results obtained on the adsorption and desorption behaviour of HM on coal fly ash can be explained in part on the basis of the surface predominance and the aqueous chemistry of single ionic, mainly anionic, forms of the relative elements. But ion exchange and coprecipitation phenomena also seem to be important processes. The nature and concentration of ions contained originally in the water used (distilled water, fly ash leachate and seawater) were found to have a strong influence on the sorptive behaviour of HM on coal ashes. The high degree of applicability of radiochemical and nuclear techniques to coal ash water leaching problems has been demonstrated and further points for subsequent research in this field possibly using nuclear techniques are indicated.

The Elimination of Mineral Micropollutants

Mineral micropollutants in waste waters and drinking water are essentially composed of heavy metal salts. Their elimination, when present in trace quantities, is discussed in this paper. The techniques, which water treatment facilities can use, necessitate preclarification in open basins (efficiency varying between 20 and 90%), elimination by filtration, with efficiencies depending largely on preoxidation but particularly on coagulation-precipitation and related techniques. Our investigations, as well as certain literature data, demonstrate the predominating importance of contact between water and sludges in decanters-clarificators. Thus, Jar tests often yield only a poorly representative result of the elimination of heavy metals by coagulation-flocculation-decantation. As to the use of aluminium sulphate, for example, the elimination rates mentioned relating to the elimination rate or % removal in laboratory experiments, in pilot tests with sludge beds and in treatment plants respectively are as follows: Fe: 100, 95, 100; Mn: 4, 38, 97; Cu: 91, 83, 85; Cr: 29, 8, 83; Cd: 21, 29, 96; Ni: 0, 20, 50; Co: 0, 16, 51; Pb; -, 52, 61. It should be noted that treatment in plants is much more elaborate (oxidation by chlorine dioxide, application of activated silica and a one hour contact time with the sludge bed) than in pilot experiments (15 minutes contact time and a sludge bed without activated carbon). The oxidation state of metals plays an important role in techniques for their elimination by the usual methods such as coagulation-flocculation-decantation as well as in coprecipitation phenomena of Fe and Mn for example. The method of alkaline precipitation, in which the pH value needed is obtained by addition of lime, results in elimination rates over 80% and generally far over 90%. This method uses at the same time direct precipitation and coprecipitation in a calcium carbonate/magnesium oxide matrix. Ion exchange gives highly variable elimination results according to the ion present and its concentration. In practice, strong cation exchange resin are generally applied. In treatment plants, adsorption on carbon allows an overall yield of 50-100% removal of the metal concerned, provided that preoxidation and sufficient contact times are allowed. The experimental distinction of the specific effect due to adsorption is difficult, but according to our studies, adsorption occurs to a small extent only in the majority of cases. 30-50% of the remaining traces are eliminated by infiltration of purified waters underground, where a levelling of concentrations also occurs. In addition to the investigations presented, studies still being carried out demonstrate a sufficient stabilization of heavy metals immobilized with lime in order to allow them to be dumped in the environment without risk. This method seems confirmed as a method of choice in treatment of waste waters loaded with heavy metals.

Geochemical soil prospecting in Northwest Kalimantan, Indonesia

A target area in northwestern Kalimantan, Indonesia, already defined by a geochemical stream-sediment survey, has been further investigated by geochemical analysis of soils and samples of test pits. Overlapping geochemical anomalies in the soils were found for Cu, Mo, Au and Bi. Anomalies and high values of the other elements, Pb, Zn, Fe, Mn and As, can be explained by lithology and by scavenging and coprecipitation phenomena at the break of slopes. With the aid of detailed geochemical mapping and mineralogical and petrographic analysis the Cu-Mo-Au-Bi anomaly was explained by a porphyry-type mineralization consisting mainly of chalcopyrite and molybdenite within a quartz-enriched granodiorite. Hydrothermal alteration consists of a potassic zone, including the anomaly, and a broad propylitic zone. This type of mineralization is related to the plate-tectonic evolution of Sundaland. The possibility of a belt of porphyry-type mineralization in western Kalimantan is proposed.