Addition Of Tartaric Acid Research Articles

Visible-light-driven 3D hierarchical Bi2S3/BiOBr hybrid structure for superior photocatalytic Cr(VI) reduction

The most important approach to eliminate poisonous Cr(VI) from water utilizing visible-light photocatalytic activities is the reduction of highly toxic Cr(VI) to less harmful Cr(III). In this study, a facile one-pot homogenous precipitation method was designed for the first time to fabricate the heterojunction of Bi2S3/BiOBr. The hybrid structure was characterized using XRD, FE-SEM, EDS, TEM, UV–vis (DRS), XPS, and PL. The synthesized heterostructure confirmed the successful anchoring of Bi2S3 nanoparticles onto BiOBr nanosheets. The as-prepared Bi2S3/BiOBr hybrid structure exhibited significantly enhanced photocatalytic performance for the reduction of Cr(VI) to Cr(III) compared with pure BiOBr that confirmed by XPS analysis after 10 min. The hybrid structure of Bi2S3/BiOBr showed a superior rate constant 10 times higher than that for pure BiOBr. Moreover, the reduction efficiency of Cr(VI) solution containing 50 mg/L was improved up to 99.2% within 40 min by the addition of tartaric acid as a hole scavenger. The reduction efficiency of different photocatalysts towards Cr(VI) removal from the real sample was also examined. The Bi2S3/BiOBr hybrid structure can be reused after regeneration process without a significant loss in photoreaction behavior after four recycle runs.

Prestretching effect and recovery process of polyvinyl alcohol film crosslinked with tartaric acid

AbstractThe tartaric acid (TA)/polyvinyl alcohol (PVA) composite films were prepared with various TA concentrations from 5 to 20 wt%. The crosslinking due to TA improved the tensile characteristics such as tensile strength and the Young's modulus, and thermal stability of the films. The addition of TA in PVA led to a decrease in the crystallinity. Application of prestretching or preliminary deformation resulted in significant changes in both stress–strain behavior and tensile characteristics of both pure PVA and TA/PVA composite films. Although low preextension levels such as 5% strain did not change much the tensile characteristics, higher preextension levels improved the tensile strength but decreased the extensibility of the films. The recovery processes of the stretched films consisted of a fast recovery process for which most of the recoverable elastic deformation is seen took place within almost 30 min and a time‐dependent long‐lasting recovery process continued in time very slowly, which resulted in undesirable residual deformation. It was also observed that increasing TA concentration accelerated the recovery process, hence, improved the recovery properties of PVA. The use of TA in the membrane applications can be considered to improve the mechanical properties and reusability of the membrane technology.

Tartaric acid enhanced CuFe2O4-catalyzed heterogeneous photo-Fenton-like degradation of methylene blue

CuFe2O4 particles were obtained by sol-gel process and characterized by XRD, SEM and EDS. The effects of tartaric acid (TA) on the degradation of methylene blue (MB) were studied in the presence of CuFe2O4 and H2O2 under light irradiation. The results showed that introducing TA enhanced MB decolorization rate from 52.0% to 92.1% within 80 min. The contribution of superoxide anions (O2−) was only 10% and the contribution of hydroxyl radical (OH) was around 88%. For H2O2-CuFe2O4-photo system, in the presence (or absence) of TA, the dynamic change of OH suggested that the addition of TA could promote the generation of hydroxyl radicals. The enhanced effect of TA in TA-H2O2-CuFe2O4-photo system could be attributed to its own structure and the dissolved metal ions of the catalyst surface. In addition, a reasonable mechanism for the complex system was elucidated.

Electroplating and Characterization of Invar Fe–Ni Alloy Films from Plating Baths Containing Organic Acids

In Fe–Ni alloys, coefficients of thermal expansion (CTEs) of Fe–Ni alloys with 30 to 45 mass% Ni are small compared to that of Fe (CTE = 12 ppm/K) or Ni (CTE = 13 ppm/K) at near room temperature. In particular, the Fe–Ni alloy with 36 mass% Ni exhibits the lowest CTE (approximately 1 ppm/K) among the Fe–Ni alloys. These Fe-Ni alloys with 30 to 45 mass% Ni are called “Invar alloys.” The Fe–Ni alloy electroplating can allow lower cost of Invar alloy production compared with the conventional rolling process. Furthermore, the electroforming process can provide precise micrometer-sized three-dimensional structures of Invar alloys with excellent thermal dimensional stability, e.g., MEMS (microelectromechanical systems). An acidic Fe–Ni alloy electroplating bath usually contains an organic acid, which acts as a masking agent for Fe3+ generated via electrochemical and air oxidation and pH buffer agent. However, it is known that an organic additive addition often effects on properties, e.g. internal stress in the Fe–Ni alloy electroplated films. For MEMS applications in particular, internal stress should be minimized. So far, the internal stresses in the electroplated Fe–Ni alloy films in the Invar composition range obtained from the alloy plating baths containing various organic acids have not been studied in detail. In this study, we investigated the influence of the type of organic acid added to the alloy plating bath on composition, current efficiency and internal stress in the Fe–Ni alloy films electroplated from various Fe2+ concentration baths. Electroplating of the Fe–Ni alloy was carried out using sulfate/chloride bath (modified Watts-type Ni plating bath) with additives at a current density of 40 mA/cm2. Bath compositions were as follows: FeSO4 (0 to 0.4 mol/L), NiSO4 (0.95 mol/L), NiCl2 (0.17 mol/L), boric acid (0.49 mol/L), sodium saccharin (0.008 mol/L) and organic acid (0.05 mol/L). Organic acids were selected based on the stability constant (log KMA) of the complex with Fe3+: tartaric acid (log KMA = 6.49), malonic acid (log KMA = 7.52), or citric acid (log KMA = 11.5). The bath temperature was maintained at 50 °C and the bath pH was adjusted to pH 2.5. Pure Ni sheets were used as anodes. Internal stress in the films was estimated by the bending strip method using a Cu–Be foil as a substrate, and the value of internal stress was calculated based on Stoney’s equation. The composition of the electroplated Fe–Ni alloy film was determined by the fundamental parameter method. Regardless of the presence or absence of an organic acid, the Fe content in the electroplated Fe–Ni alloy film increased with the increase in the concentration of Fe2+ in the plating bath, and at the Fe2+ concentration of 0.3 to 0.4 mol/L, Fe–Ni alloy electroplated film with a Ni content of 30 to 45 mass%, in the Invar composition range, was obtained. Without addition of an organic acid, current efficiency showed high efficiency of 95 % or more at any Fe2+ concentration. In contrast, the current efficiency decreased to approximately 90 % due to the addition of the organic acid. Citric acid added bath exhibited lower current efficiency than those form baths with tartaric acid or malonic acid at the Fe2+ concentration of 0.3 to 0.4 mol/L. The decrease in the current efficiency in the Fe–Ni alloy plating reaction was related to hydrogen evolution as a side reaction. Organic acids promoted hydrogen evolution during Fe–Ni alloy plating reaction. Citric acid most promoted hydrogen evolution at 0.3 to 0.4 mol/L of Fe2+ to obtain an Invar Fe–Ni alloy electroplated film. Without addition of saccharin, micro cracks occurred in the Invar Fe–Ni alloy electroplated films because the films generated very large internal stresses (tensile). Addition of tartaric acid or malonic acid to Fe–Ni alloy plating bath including saccharin kept the internal stress in Invar Fe–Ni alloy electroplated film relatively low (tensile, approximately 200 MPa), and furthermore, may prevent a decrease in toughness of the film by masking Fe3+. Consequently, these optimized Invar plating baths can be used for MEMS electroforming. In contrast, due to the addition of citric acid to form a more stable complex with Fe3+, internal stresses in the Invar Fe-Ni alloy electroplated films became very high (tensile, 300 MPa or more) and micro cracks occurred in the films; it was difficult to provide the obtained films as MEMS materials. It is expected that the internal stress behavior in the Invar electroplated films depending on the type of organic acid added to bath will be related to hydrogen evolution and impurity incorporation to the film during the Invar electroplating.

Electroplating and Characterization of Invar Fe–Ni Alloy Films from Plating Baths Containing Organic Acids

Practical plating baths and plating conditions for preparing Fe–Ni alloy electroplated films with compositions in the Ni content range 36–100 mass% have been proposed. The addition of saccharin in sulfate-chloride bath is indispensable for preparation of Fe-30–45 mass% Ni alloy electroplated films, i.e., those in invar composition region. The addition of tartaric acid or malonic acid to Fe–Ni alloy plating baths (containing saccharin) prevents a reduction in the toughness of the plated film by masking Fe3+ generated by oxidation. It was possible to suppress the internal stress in invar Fe–Ni alloy electroplated films to low levels. Resultantly, the invar electroplated films obtained from these optimized plating baths show promise for electroforming. On the contrary, the addition of citric acid, which forms a more stable complex with Fe3+, causes very large internal stress in the resultant invar Fe–Ni alloy electroplated films, making them unsuitable as MEMS materials. It was confirmed that Fe–Ni alloy electroplated films with Ni contents of 45–100 mass% comprise a single-phase alloy having an fcc structure but the invar Fe-36–42 mass% Ni alloy electroplated film is a metastable bcc phase or a mixture of bcc and fcc phases. Therefore, to impart low thermal expansion characteristics to as-plated invar alloy films, it is necessary to induce phase transformation to an fcc phase, which is the equilibrium phase at high temperature, by the means of heat treatment.

Electrochemical Reduction of Bi(III)/Sb(III)/Te(IV) with EDTA and Tartaric Acid in Sulfuric Acid Solution

The electrochemical reduction of Bi(III), Sb(III) and Te(IV) with EDTA and tartaric acid complexing agents in sulfuric acid solution were studied by linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) separately. The results reveal that the addition of EDTA makes the reduction potential of Bi(III) shift negatively, but does not affect the reduction potential of Sb(III) and Te(IV), which makes the deposition potential of Bi(III), Sb(III) and Te(IV) close to each other. The addition of tartaric acid makes the reduction potential of Bi(III) negatively shift a little and the reduction potential of Sb(III) shift negatively, but does not affect the reduction potential of Te(IV), which makes the deposition potential of Bi(III), Sb(III) and Te(IV) far away from each other. Meanwhile, the role of EDTA is to increase the solubility of Bi(III), and tartaric acid is expected to improve the solubility of Sb(III), EDTA and tartaric acid could enhance the stability of Bi(III)-Sb(III)-Te(IV) ternary mixture.

Addition of tartaric acid to prevent delayed setting of oil-well cement containing retarder at high temperatures

The setting time of the cement containing retarder at high temperature is longer than that at low temperature, which is an abnormal phenomenon and is adverse to the safety of cementing operation. Several kinds of retarders were chosen to demonstrate the abnormal phenomenon and to select the retarder with the ability to eliminate the abnormal phenomenon. Tartaric acid was found to be the only retarder which did not show the abnormal phenomenon. Moreover, it could eliminate the abnormal phenomenon of the cement containing a copolymer retarder. In addition, tartaric acid may also eliminate the abnormal phenomenon in cement containing other retarders, and it may be used with other retarders together to develop a compound retarder without the phenomenon of slow setting at high temperature. The elimination mechanism of the abnormal phenomenon was studied by comparing the hydration products of the cement containing AMPS-IA with the cement containing tartaric acid using XRD. Based on the results, there was a reduction in the hydration rate difference of tetra calcium aluminoferrite (C4AF) between low and high temperatures after introducing tartaric acid, which could be the reason why tartaric acid could eliminate the abnormal phenomenon.

Electrodeposition of p-Type Sb₂Te₃ Films and Micro-Pillar Arrays in a Multi-Channel Glass Template.

Antimony telluride (Sb2Te3)-based two-dimensional films and micro-pillar arrays are fabricated by electrochemical deposition from electrolytes containing SbO+ and HTeO2+ on Si wafer-based Pt electrode and multi-channel glass templates, respectively. The results indicate that the addition of tartaric acid increases the solubility of SbO+ in acidic solution. The compositions of deposits depend on the electrolyte concentration, and the micro morphologies rely on the reduction potential. Regarding the electrolyte containing 8 mM of SbO+ and 12 mM of HTeO2+, the grain size increases and the density of films decreases as the deposition potential shifts from −100 mV to −400 mV. Sb2Te3 film with nominal composition and dense morphology can be obtained by using a deposition potential of −300 mV. However, this condition is not suitable for the deposition of Sb2Te3 micro-pillar arrays on the multi-channel glass templates because of its drastic concentration polarization. Nevertheless, it is found that the pulsed voltage deposition is an effective way to solve this problem. A deposition potential of −280 mV and a dissolve potential of 500 mV were selected, and the deposition of micro-pillars in a large aspect ratio and at high density can be realized. The deposition technology can be further applied in the fabrication of micro-TEGs with large output voltage and power.

Lachancea thermotolerans Applications in Wine Technology

Lachancea (kluyveromyces) thermotolerans is a ubiquitous yeast that can be naturally found in grapes but also in other habitats as soil, insects and plants, extensively distributed around the world. In a 3-day culture, it shows spherical to ellipsoidal morphology appearing in single, paired cells or short clusters. It is a teleomorph yeast with 1–4 spherical ascospores and it is characterized by a low production of volatile acidity that helps to control global acetic acid levels in mixed or sequential inoculations with either S. cerevisiae or other non-Saccharomyces species. It has a medium fermentative power, so it must be used in sequential or mixed inoculations with S. cerevisiae to get dry wines. It shows a high production of lactic acid able to affect strongly wine pH, sometimes decreasing wine pH by 0.5 units or more during fermentation. Most of the acidification is produced at the beginning of fermentation facilitating the effect in sequential fermentations because it is more competitive at low alcoholic degree. This application is especially useful in warm areas affected by climatic change. pH reduction is produced in a natural way during fermentation and prevents the addition of tartaric acid, that produces tartrate precipitations, or the use of cation exchangers resins highly efficient reducing pH but with undesirable effects on wine quality. Production of lactic acid is done from sugars thus reducing slightly the alcoholic degree, especially in strains with high production of lactic acid. Also, an improvement in the production of 2-phenylethanol and glycerol has been described.

Tartaric acid assisted carbonization of LiFePO4 synthesized through in situ hydrothermal process in aqueous glycerol solution

An in situ hydrothermal synthesis process was explored to prepare nano-sized high performance lithium iron phosphate carbon composite (LFPin/C) as active cathode material for lithium ion batteries. Tartaric acid (TA), as chelating agent and carbon source, was added into glycerol/water solution forming a homogeneous precursor. The mixture was transferred to a hydrothermal reactor to take full advantage of the synergistic interaction between both organic compounds in the synthesis of LFPin/C. For comparison, the properties of the ex-situ synthesized LFPex/C composite, obtained by addition of TA after the hydrothermal step, were evaluated.Results of comparative experiments show that the in situ method is capable to improve the homogeneity and dispersity of the residual carbon in combination with calcination at 600 °C for 3 h. Cyclic voltammetry and electrochemical impedance spectroscopy showed that the in situ generated carbon matrix with embedded LiFePO4 particles can reduce the charge transfer resistance. LFPin/C features a large specific surface area of 22.3 m2 g−1 and uniform particle size distribution with a typical size in the range of 20–40 nm. In line with these advantages, the composite yields excellent cycle stability with initial discharge capacities of 166.1, 140 and 104 mAh g−1 at rates of 0.1 C, 2 C and 10 C, respectively.

Influence of small concentration addition of tartaric acid on the 220 °C hydrothermal synthesis of hydroxyapatite

The synthesis of elongated hexagonal shape crystalline hydroxyapatite (HA) by chemical precipitation and crystallization by hydrothermal method at 220°C is presented, with addition of tartaric acid (TA) in small concentrations. In order to study the influence of tartaric acid addition, it was added either at the end of the precipitation stage, or to the Ca precursor (before the P precursor addition), in different molar ratios to the Ca and P precursors, whose molar ratio was kept constant. The phase identification was performed by XRD and FTIR; size and morphology was studied by means of SEM and TEM. The crystallization took place along the c crystallographic axis, with formation of lamellar crystals with hexagonal habit, whose dimensions first decrease with rising tartaric acid concentration and then increase again. The morphology of the HA crystallites changes above a certain amount of tartaric acid admixture. The addition of TA to the Ca precursor, compared to the case of its addition to the already precipitated HA, leads to better results regarding crystallinity.

The hydration mechanism and performance of Modified magnesium oxysulfate cement by tartaric acid

Magnesium oxysulfate (MOS) cement has the advantages of light weight, low alkalinity, fire resistance, and good decorative value. Large-scale applications of MOS cement in civil engineering have been restricted by its low strength, which can be improved by adding some proper additives. Here, the effects of tartaric acid on the setting time, compressive strength, flexural strength, and deformation of MOS cement have been studied. Fourier transform infrared spectra, pH changes, hydration-heat release rate, and impedance have been observed to determine the effects of tartaric acid on the hydration process of MOS cement. To a certain extent, the addition of tartaric acid extends the setting time of MOS cement by improving the stability of the hydration film of active MgO in magnesium sulfate. X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry were used to examine the hydration products and pore-size distribution of MOS cement. The analysis results indicate that the main reason for the high strength of MOS cement with tartaric acid is that the addition of tartaric acid can promote the formation of the needle-like high-strength phase of 5Mg(OH)2·MgSO4·7H2O and inhibit the formation and growth of the Mg(OH)2 crystal phase.

Effect of tartaric acid on anodic behaviour of titanium alloy

Anodic oxidation of titanium alloy Ti–6·5Al–1Mo–1V–2Zr was carried out in sulphuric acid and tartaric acid/sulphuric acid. The effect of tartaric acid on the growth process of sulphuric anodic film on titanium alloy was evaluated using scanning electron microscope, atomic force microscope, Raman spectroscope, inductively coupled plasma mass spectroscope and X-ray photoelectron spectroscope. The presence of tartaric acid in sulphuric acid reduced the crystallinity of the anodic film and decreased the intensity of oxygen evolution in the pores of the anodic film. Further, the dissolution rate of the anodic film was also reduced by the addition of tartaric acid. Therefore, the growth rate of the anodic film on the titanium alloy was accelerated by the addition of 40 g L−1 tartaric acid in sulphuric acid electrolyte.

Physical and structural characterisation of starch/polyester blends with tartaric acid

Starch/PBAT blends were produced by reactive extrusion with tartaric acid (TA) as an additive. The effects of TA, glycerol and starch+PBAT on the mechanical, optical and structural properties of the films were evaluated, with formulations based in a constrained mixture design. Tartaric acid acts as a compatibiliser and promotes the acid hydrolysis of starch chains. These two functions explain the observed film resistance and opacity. TA reduced the weight loss in water. Scanning electron microscopy (SEM) images showed that TA reduces the interfacial tension between the polymeric phases, resulting in more homogeneous films. Nuclear magnetic resonance (13C CPMAS) and Fourier transform infrared spectroscopy (FT-IR) suggest that tartaric acid is able to react with the hydroxyl groups of the starch by esterification/transesterification reactions, confirming its role as a compatibiliser. The addition of TA results in materials with better properties that are suitable for use in food packaging.

Development of Cerium-Rich Layers on Anodic Films Formed on Pure Aluminium and AA7075 T6 Alloy

The development of cerium-rich layers on anodized pure aluminum and AA7075 T6 aluminum alloy has been investigated using scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The surfaces of pure aluminum and AA7075 T6 were pre-treated by alkaline etching and HNO3 desmutting followed by anodizing in sulfuric acid electrolyte with and without addition of tartaric acid. The outer layer is created by immersion in a cerium (III) nitrate solution containing hydrogen peroxide. It is shown that anodizing in a mixture of sulfuric and tartaric acids prior to the immersion treatment leads to the formation of a thicker and a more uniform cerium-rich layer. The ultramicrotomed sections display the presence of cerium species within the pores of the anodic film. This treatment significantly improves the corrosion resistance of the material.

Uranium uptake in Nicotiana sp. under hydroponic conditions

The effect of pH, phosphates, organic acids (citrate, tartarate, oxalate) and polyamines on uptake and translocation of uranium was followed in Nicotiana tabacum L. seedlings. Transport of uranium to upper, harvestable parts was very limited. The absence of phosphates generally increased the uptake and transfer of uranium from the roots to the shoots. The addition of tartaric acid increased the translocation of uranium, especially simultaneously with the phosphate absence. Higher uptake of uranium was also observed at pH3.5 (acetic acid), although the translocation was lower. The spraying with polyamines (putrescine, cadaverine, spermine and spermidine) resulted in moderate decrease of uranium content in the leaves and the roots, which was still significant, except of spermine in roots. Our results showed that the composition of the cultivation media can significantly affect uranium accumulation and its distribution within the plants. Thus, the potential of uranium accumulation in harvestable plant parts can be significantly enhanced.

Effect of trace tartaric acid on anodizing of etched aluminum foil for high voltage electrolytic capacitor

The effects of the addition of trace amounts of tartaric acid to the boric acid electrolyte on the microstructure and electrochemical performance of anodized aluminum foils with a tunnel etch structure for high voltage electrolytic capacitors are studied with TEM, XRD, EIS, LCR meter and small-current charging. The results show that the high voltage anodized oxide film consists of an inner layer with high crystallinity and an outer layer with low crystallinity. The addition of tartaric acid can effectively promote crystalline anodic oxide formation and obtain a barrier film with a high degree of crystallinity, thereby enhancing the film capacitance and field strength. However, more intrinsic defects such as cavities, slits and voids occur due to severe phase transformation and shrinkage, thereby reducing the film resistance and withstanding voltage.

Additive effects on tin electrodepositing in acid sulfate electrolytes

The effects of additives on the stannous reduction of an acid sulfate bath were investigated using cyclic and linear sweep voltammetry, electrochemical impedance spectroscopy (EIS), and microstructure analysis. In the absence of additives, tin coatings are rough, and the tin electrodepositing is a single-step reduction process accompanied by hydrogen gas evolution. The addition of tartaric acid produces a slight reduction in the peak current of stannous reduction and has an appreciably positive effect on the stability of the acidic tin bath. Both benzylidene acetone and polyoxyethylene octylphenol ether hinder the stannous reduction and greatly suppress the hydrogen gas evolution. Formaldehyde slightly decreases the peak current density of stannous reduction and serves as an auxiliary brightener in the acid sulfate bath. The presence of mixed additives greatly suppresses the stannous reduction and hydrogen gas evolution and consequently produces a significantly smoother and denser tin coating. The (112) crystal face is found to be the dominant and preferred orientation of tin deposits.

Effect of addition of tartaric acid on synthesis of boron carbide powder from condensed boric acid–glycerin product

The effect of the addition of tartaric acid on the synthesis of boron carbide (B4C) powder from a condensed boric acid (H3BO3)–glycerin product was investigated in this study. The condensed product was prepared by dehydration condensation after directly mixing equimolar amounts of H3BO3 and glycerin with the addition of 0–50mol% tartaric acid (based on glycerin), which was followed by thermal decomposition in air to obtain a precursor powder from which excess carbon had been eliminated. The dispersion state of the boron oxide (B2O3) and carbon components in the precursor prepared from the condensed product with 25mol% tartaric acid added was finer than that without tartaric acid added, in which both precursors had a three-dimensional bicontinuous B2O3/carbon network structure. The complete formation of crystalline B4C powder was achieved at 1250°C within a shorter heat treatment time for the precursor with a fine dispersion state. The synthesized B4C powders became fine owing to the increased number of nucleation sites.

Coupling of tartaric acid-promoted soil dissolution and Cr(VI) reduction in an Oxisol

Environmental risk posed by Cr(VI)-contaminated soils could be effectively alleviated through the reduction of Cr(VI) to Cr(III) by organic compounds, which was usually limited in practical application due to the slow reaction rate. Soil surfaces have been found to catalyze many redox reactions. In this study, an Oxisol containing abundant Fe and Mn-oxides was selected to investigate the soil surfaces-catalyzed Cr(VI) reduction by tartaric acid with the aim to elucidate the coupling of soil Fe/Mn oxides dissolution and Cr(VI) reduction. In the absence of tartaric acid, the reduction of Cr(VI) by soil itself could be excluded, and only Cr(VI) adsorption onto the soil was observed, which proceeded very rapidly at the initial stage, followed by a slow progress. No measurable Cr(VI) reduction by tartaric acid was found without the addition of the soil during 24h, while Cr(VI) reduction would occur after the soil was introduced to the system. It was believed that Cr(VI) reduction mainly occurred in solutions not the solid surfaces since Cr(VI) adsorption was significantly inhibited due to the competitive effect of excessive tartaric acid and the background electrolyte. Aqueous Fe(III) and Mn(II) released from tartaric acid-promoted soil dissolution accounted for the acceleration of Cr(VI) reduction, which was also confirmed by the results from the experiments conducted in aqueous solutions. Addition of tartaric acid to soil suspensions pre-equilibrated with Cr(VI) for 24h would lead to more Cr(VI) reduced to Cr(III). This result was mainly explained as the enhancement of H+ adsorption caused by the increase in negative charge due to the Cr(VI) adsorption, which would promote the release of Fe(III) and Mn(II) from soil surfaces to solutions in turn. Moreover, desorption of the adsorbed Cr(VI) to solutions was the necessary step for the reduction of Cr(VI) adsorbed onto the soil. Part of Cr(III) generated in solutions would be adsorbed to soil surfaces, evidenced by the decrease in total aqueous Cr concentration. The present study gave some insight into the mechanisms of soil surfaces catalyzed Cr(VI) reduction by organic compounds, and were helpful for formulating the remediation strategy of Cr(VI)-contaminated soils.