Jin-Yeon Hwang

Sedimentation characteristics of two commercial bentonites in aqueous suspensions

Abstract The sedimentation characteristics of two commercial bentonites, Tixoton (organically treated) and Montigel-F (untreated), were investigated using a 3% w/v clay suspension at different concentrations (1, 3.5 and 10%) of NaCl and pH values (2, 7 and 12). Settling rates, floc diameters and sediment volumes were derived from changes in light transmittance using a Turbiscan Ma 2000 instrument. Both bentonite suspensions were unstable (flocculated) in NaCl solutions. The settling rate increased with increasing concentration of NaCl and was directly related to floc diameter. The sediment volume reduced with increasing NaCl concentrations, a result of greater double layer compression caused by increased ionic strength. At comparable salt concentrations, the organically-treated bentonite (Tixoton) settled at a much slower rate and had a greater sedimentation volume. The suspensions of both organically-treated and untreated bentonites were stable (dispersed) above pH 7 and unstable in acidic conditions. The settling rate for Tixoton under acid conditions was much smaller than that for the Montigel-F. Differences in sedimentation characteristics between the two bentonite samples are probably due to the presence of an anionic polymer (carboxymethyl cellulose: CMC) in Tixoton. The viscosity of the bentonite suspensions was also studied. The viscosity of the clay suspension is closely related to clay dispersivity in solution. The CMC was highly effective in increasing the viscosity of the bentonite suspensions, but only under neutral and alkaline conditions.

Enhancement of dissolution rates of amorphous silica by interaction with amino acids in solution at pH 4.

Amino acids are present in various geochemical environments and they interact with mineral surfaces. To evaluate the effects of amino acids on mineral dissolution at pH conditions less than their isoelectric points (pI), dissolution experiments of X-ray amorphous silica in solutions containing 10.0 mmol/L of various amino acids (cysteine, asparagine, serine, tryptophan, alanine, threonine, histidine, lysine, and arginine) at pH 4 were performed. The results confirmed that basic amino acids (histidine, lysine, and arginine) produce an 8- to 8.5-fold enhancement of the rate of dissolution of amorphous silica compared with an amino acid-free control. Neutral amino acids (cysteine, asparagine, serine, tryptophan, alanine, and threonine) enhanced rates of dissolution by a factor of ∼3 to 3.5. The rate-enhancement effects of amino acids are controlled by concentrations of the amino acid’s cationic species which interact with the negatively charged >SiO− sites at the surface of the amorphous silica.

ENHANCEMENT OF DISSOLUTION RATES OF AMORPHOUS SILICA BY INTERACTION WITH BOVINE SERUM ALBUMIN AT DIFFERENT pH CONDITIONS

Proteins and protein-like molecules are abundant in various geochemical environments; they form complexes with mineral surfaces and with dissolved organic matter. To evaluate the effect of proteins on rates of dissolution of minerals, experiments on the dissolution of amorphous silica in solutions containing various concentrations of bovine serum albumin (BSA) were performed in this study. The dissolution experiments were carried out by a batch method using solutions of 0.1 mM NaCl with 0.00, 0.05, 0.1, 0.2, 0.5, and 1.0 mg/mL of BSA at three different pH conditions, 6, 5, and 4. The results of the experiments demonstrated that BSA exhibited strong rate-enhancement effects on the dissolution of amorphous silica and were dependent on BSA concentration and the solution pH. At pH 6, the dissolution rates of amorphous silica appeared to increase successively by ~1.6, 2.2, 2.4, 2.5, and 2.9 times with increasing BSA concentrations of 0.05, 0.1, 0.2, 0.5, and 1.0 mg/mL, respectively. The rates of dissolution increased by greater degrees, ~3.1–5.8 and 4.9–13.0 times at pH 5 and 4, respectively. According to the calculated charge distributions of amino acid residues of the BSA molecule, the dissolution rates of amorphous silica were likely to be enhanced by attractive electrostatic interactions of the positively charged side chains of lysine, arginine, and histidine residues with the negatively charged >SiO− sites on the amorphous silica surface. The negatively charged side chains such as glutamic acid and aspartic acid residues may inhibit the attractive interaction, depending on the degree of deprotonation.

INFLUENCE OF GUANIDINE, IMIDAZOLE, AND SOME HETEROCYCLIC COMPOUNDS ON DISSOLUTION RATES OF AMORPHOUS SILICA

Guanidine and imidazole are important functional molecules that constitute the side chain of basic amino acids (arginine and histidine); these molecules are capable of interacting with mineral surfaces. However, little information is available about the effect of these molecules on mineral dissolution, including amorphous silica. In this study, to evaluate the effect of these organic molecules on the dissolution rates of amorphous silica, dissolution experiments were performed in solutions containing these molecules and other related heterocyclic compounds. The dissolution experiments were conducted by the batch method using 0.1 g of amorphous silica and 100 mL of 0.1 mM NaCl solution with 0.0, 0.1, 1.0, and 10.0 mM of guanidine, imidazole, pyrazole, or pyrrole at pH values of 4, 5, and 6. The results demonstrated that these compounds can enhance the dissolution rate of amorphous silica, depending on their ionic speciation in the following order: guanidine = imidazole > pyrazole > pyrrole. When 10.0 mM solutions were used, both guanidine and imidazole greatly increased the dissolution rate with an enhancement factor of 5.5—6.5, pyrazole exhibited a smaller change in the dissolution rate with an enhancement factor of 1.5—2.4, and pyrrole exhibited no significant enhancement. ChemEQL calculations confirmed that guanidine (pK = 13.6) and imidazole (pK = 6.99) are fully protonated and mostly present as cationic species in a pH range of 4—6; therefore, these compounds are capable of interacting with the >SiO- sites of amorphous silica. Pyrazole (pK= 2.61) and pyrrole (pK = 0.4), however, existed mostly as neutral forms. The concentrations of cationic species of pyrazole and pyrrole were at least one and three orders of magnitude lower than those of fully protonated compounds, respectively; therefore, pyrazole and pyrrole were less reactive than the fully protonated compounds on the surfaces of amorphous silica.

The Relationship between the Mineral Characteristics and Spectral Induced Polarization for the Core Rock Samples from the Gagok Skarn Deposit

In order to develop the evaluation techniques for the potential sulfide ore reserves, the relationships between the modal vol.%, grain sizes and textural characteristics of the constituent minerals (e.g., sulfides, oxides and skarn minerals) and the Spectral Induced Polarization (SIP) phase differences are examined for the nine rock cores collected from the Gagok Pb-Zn skarn deposit. The Gagok Pb-Zn skarn deposit occurs mainly along the intrusive contact between the Cretaceous granitic rocks and Cambrian Myobong slate and Pungchon limestone. The nine rock cores have been grouped into three showing distinctive SIP phase differences: the highest (Group I), intermediate (Group II) and lowest (Group III). In relation with the modal vol.% of minerals, Group I is characterized by higher pyrrhotite (25-38 vol.%) and amphibole (40-55 vol.%); Group II by intermediate pyrrhotite (7-13 vol.%) and higher garnet (44-68 vol.%); and lower pyrrhotite (1-7 vol.%) and higher pyroxene (24-66 vol.%) stand for Group III. Furthermore, the grains of all the major constituent minerals become smaller from Group I (

Occurrence and Mineralogy of Serpentinite from Bibong Mine in Chungyang Area, Korea

Six serpentine mines are found in South Korea. We investigated occurrence, characteristics and origin of constituent minerals of Bibong serpentine mine in Chungcheongnam-do. We also analyzed the properties of serpentine minerals using XRD, XRF, SEM/EDS, FT-IR, EPMA and polarized microscope. The serpentinite of Bibong mine occurs as intruded body within the Precambrian metasedimentary rocks. Various minerals such as serpentine, forsterite, pyroxene, tremolite, magnetite, chlorite, mica, talc and dolomite are occurre. Five distinctive mineral assemblage types are observed in the serpentinite: (A) serpentine-forsterite, (B) serpentine, (C) serpentine-chlorite (vermiculite), (D) serpentine-tremolite, (E) tremolite-chlorite. Lizardite and antigorite are mainly occurred as serpentine minerals and chrysotile is partly included. From the study of mineral compositions and occurrence of serpentinite body, serpentine formed by hydrothermal alteration of ultramafic rock consisting mainly of forsterite, and altered minerals such as chlorite and tremolite subsequently formed by secondary hydrothermal alteration.

A Preliminary Study of Rodent Burrows at Lake Hovsgol, Mongolia: Comparison with the Late Pleistocene Rodent Burrows of Korea

In this study, we investigated the characteristics of rodent (mainly ground squirrel) burrows found near the Lake Hovsgol, Mongolia. Those burrows are straight to slightly curved and gently inclined in lateral view. Cross-sectional shapes are either circular or elliptical with diameters ranging from mostly 8-10 cm. Most abandoned burrows are passively filled with soils and/or pebbles. The size and architecture of these Mongolian burrows are remarkably similar to those of the previously reported Late Pleistocene burrows from Korea. Therefore, the rodent burrows found at Korean Palaeolithic sites are thought to have been formed by ground squirrels. However, the difference in burrow-fills suggests that the mean annual precipitation of the Korean Peninsula during the Late Pleistocene is much higher than that of Mongolia.

Preventive Measures on Alkali-Silica Reaction of Crushed Stones

In Korea, due to the insufficiency of natural aggregates and increasing needs of crushed stones, it is necessary to examine the alkali-silica reaction of the crushed stones. The reaction produces an alkali-silica reaction gel which can imbibe pore solution and swell to generate cracks that are visible In affected concrete. In general, crushed stones are tested by petrograptuc examination, chemical method and mortar-bar method, but the most reliable method Is mortar-bar test. This study tested alkali-silica reactivity of crushed stones of various rock types using ASTM C 227 and C 1260, and compared the results of two test methods. This study also analyzed effects of particle size and grading of reactive aggregate on alkali-silica reaction expansion of mortar-bar. The effectiveness of mineral admixtures to reduce detrimental expansion caused by alkali-silica reaction was investigated through the ASTM C 1260 method. The mineral admixtures used were nv ash, silica fume, metakaolin and ground granulated blast furnace slag. The replacement ratios of 0, 5, 10, 15, 25 and were commonly applied for all the mineral admixtures and the replacement ratios of 45 and were additional applied for the admixtures that could maintain workability. The results indicate that replacement ratios of for ay ash, for silica fume, for metakaolin or for ground granulated blast furnace slag were most effective to reduce alkali-silica reaction expansion under the experimental conditions.