Low-grade Clay Research Articles

Composition, Geotechnical Characteristics and the Potential for Industrial Use of Some Clay Bodies in Obudu and its Environs, Southeastern Nigeria

Samples of clay deposits in Obudu and its environs, southeastern Nigeria were evaluated to establish their potential for industrial use. Geochemical, mineralogical and geotechnical properties were employed in assessing the suitability of the clay deposits for potential industrial uses. Mineralogical analyses reveal kaolinite as the dominant clay mineral with quartz as the dominant non-clay mineral. The physical and geotechnical properties indicate that the hydrous and marginal expansive clays are fine-grained (75 μm > 2%), have low to medium plasticity (plasticity index 12.8–40.8%), low density (1.69 to 2.60 g/cm3) and low linear shrinkage (4–6%) on drying and firing. Geochemical analysis shows significant amounts (> 1.0 wt%) of SiO2, Al2O3, Fe2O3, MgO, CaO, and Na2O, and relatively low values (< 1.0 wt%) of K2O, FeO and TiO2. The clays meet the requirements for production of building bricks, roofing tiles, local pottery products and domestic ceramic wares other than ceramic white wares. However, these low grade clays will require a high degree of refining or beneficiation to remove the undesirable minerals to qualify for use in rubber, paper, paint and cosmetic industries.

Increasing the kaolinite content of raw clays using particle classification techniques for use as supplementary cementitious materials

The adoption of blended cements to reduce the carbon footprint has increased significantly over the last decades. Clays containing kaolinite are a promising choice due to their widespread availability. Kaolinite content is the major factor controlling the performance of blended cements incorporating calcined clay, for example in LC3-50 (50% clinker, 30% calcined clay, 15% limestone and 5% gypsum) clays with a kaolinite above about 40% are needed to achieve similar strength to reference OPCs at 7 days. Materials with low contents of kalinite are often considered unsuitable. This study compares two fractionation techniques to increase the kaolinite content of a low-grade clay (30% kaolinite content). The results show that kaolinite remains concentrated in the fine particles after grinding. Both wet sedimentation and air separation were effective to increase the reactivity of the material as a combined result of increased fineness and kaolinite content. For the air separation process, it was observed that a significant amount of kaolinite remained in the rejected fraction after processing due to agglomeration of the powder. It was shown that the use of grinding aids before the separation process can further improve the results.

Calcined low-grade multimineral clays as supplementary cementitious materials: a feasibility study

ABSTRACT The relevance of calcined clays as sources with great potential for low-clinker blended Portland cements has significantly increased in recent decades. This article reports on a study to evaluate the potential of the two low-grade clays containing 9.37% of montmorillonite/chlorite and 12.26% of montmorillonite/kaolinite/chlorite accompanied with 29.73% and 32.79% of calcite, respectively, as supplementary cementitious materials. The clays after thermal treatment at 800°C demonstrated poor pozzolanic activity, slight increase in the C-(S)-H and decline in the CH contents, and decrease in the mechanical properties of the blended Portland cement pastes. The results showed that the investigated clays fall below the range of the clays suitable for pozzolan production.

Structural Modification of Ceramic Brick with Multi-Walled Carbon Nanotubes

The paper considers a method for improving physical and mechanical properties of ceramic bricks made from low-melting low-grade clay and quartz sand. The priority task is to develop a kind of batch based on widespread low-grade clay containing less than 13.5% of Al2O3. This provides high physical, technical and operational characteristics of brick. To improve the properties of ceramic building materials, multi-walled carbon nanotubes (MWCNTs) can be used as an effective structural modifier in an amount of 0.001-0.009% of the clay mass. Adding an aqueous dispersion of MWCNTs to the composition of ceramic batch increases the density and uniformity of the structure of ceramic matrix and influences its strength characteristics. The increase in the strength indices of ceramic has been found to occur in both cases of using freshly prepared batch and batch seasoned for a long time, up to 6 months. Nanotubes already influence the strength of the samples at the stage of air brick forming, while the compressive strength increases by 50%. After firing, the compressive strength of fired modified samples increases by 109%. Thus, using an aqueous dispersion of MWCNTs improves the structure and physical and mechanical properties of ceramic brick.

Features of structure formation of modified composition materials

A new method for producing a composition material based on low-grade clays and dolomite was developed. Its essence lies in the fact that the clay-dolomite composition material is made using ceramic technology but hardens as a binder in the subsequent hydraulic conditions. For producing clay-dolomite composition material, fusible clays of the Absheron deposit and dolomites of the Gobustan deposit are used. The influence of various factors: the degradation kinetics of carbonates during firing, mineralizers, related phases in the rocks used, firing temperature and duration, hydraulic treatment duration, etc. on strengthening of clay-dolomite composition materials was found and their hardening mechanism was revealed. Calcium hydroxide, obtained during clay-dolomite mixture firing in the presence of smaller cations (Mg, Al) forms compounds, having binding properties, with Si 2 O 5 radicals. Such calcium silicates have layered structures and become stable only in the presence of water. It was found that the clay-dolomite composition materials gain sufficient strength after firing due to the formation of silicates, aluminum silicates and calcium and magnesium aluminates, which in their subsequent hardening in water conditions show binding properties, are hydrated to form hydrated compounds, leading to a significant increase in the composition strength.

저급 점토와 석탄회를 이용한 숏크리트용 골재의 제조

본 연구에서는 인공골재를 제조하기 위하여 저급 점토에 석탄회(Fly Ash와 Bottom Ash)를 각각 첨가하여, 여러 분석기기(SEM, XRD, XRF, TG-DTA, Dilatometer, UTM)를 이용하여 물리 화학적 특성을 조사하였다. Fly ash, bottom ash, clay의 화학조성은 <TEX>$SiO_2$</TEX>가 33.01, 53.73 및 68.36 wt% <TEX>$Al_2O_3$</TEX>는 28.54, 32.42 및 18.12 wt%와 이외에 <TEX>$Fe_2O_2$</TEX>와 알카리 성분 등이 함유하고 있다. 소성에 의한 인공골재의 치밀화 과정을 관찰하기 위해 Dilatometer를 측정하였다. 시편들은 <TEX>$850^{\circ}C$</TEX> 부근에서 서서히 수축이 시작되어 <TEX>$1100^{\circ}C$</TEX> 부근에서 급격하게 수축하는 것을 볼 수 있었다. 소성온도와 배합조성에 따른 시편의 결정상을 알아보기 위하여 <TEX>$1150^{\circ}C$</TEX>에서 30분간 열처리 하였으며 fly Ash를 사용한 시편의 주 결정상은 quartz, anorthite, albite상이 관찰되었고 bottom ash를 사용한 시편은 quartz, anorthite, mullite가 관찰되었다. <TEX>$1150^{\circ}C$</TEX>에서 소성한 시편에서 플라이애쉬 보다 바탐애쉬를 첨가한 시편이 압축강도가 우수 하며, 바탐애쉬 첨가한 시편의 경우 압축강도 87.5 kgf/<TEX>$cm^2$</TEX>로 가장 우수 하였으며 인공골재로의 이용이 가능함을 알 수가 있다. In this study, the artificial coarse aggregate was manufactured by using coal ash and low grade clay. The characteristics of a coal ash-clay system were investigated using XRD, XRF, TG-DTA, SEM and Dilatometer with various coal ash contents. The chemical compositions are the fly ash, bottom ash and clay, <TEX>$Al_2O_3$</TEX> are 28.5 wt%, 32.4 wt% and 18.1 wt%, and <TEX>$SiO_2$</TEX> are 33.0 wt%, 53.7 wt% and 68.4 wt% in weight ratio, respectively. The shrinkage of specimens started at around <TEX>$850^{\circ}C$</TEX> and changed little up to <TEX>$1100^{\circ}C$</TEX>, but increased markedly at above <TEX>$1100^{\circ}C$</TEX>. The shrinkage rate is strongly related to the decarbonization amount of coal ash. At the sintering temperature <TEX>$1150^{\circ}C$</TEX>, it was found that quartz, mullite, anorthite and albite phase exist in all specimens. It was found that bottom-clay system specimen sintered at <TEX>$1150^{\circ}C$</TEX> had a good compressive strength of 87.5 kg/<TEX>$cm^2$</TEX>, and the compressive strength of bottom-clay specimen was higher than that of fly-clay system specimen. The reusability of coal ash as a raw material in the process of shotcrete resources such as artifical coarse aggregate is highly expected.

Activación de arcillas de bajo grado a altas temperaturas

This paper introduces a proposal to produce artificial pozzolans by means of activation of low grade clays, as an alternative to metakaolin production. Basically the work considered clay mineral enriched soils, mainly kaolin. Such material was sediment and later calcined at 900 Celsius degrees. The same process was conducted with non-sediment material. Due to calcinations, the specific surface decreased significantly, and therefore, its pozzolanic activity, which was assessed by monitoring the CH consumption in cement pastes of several ages, as well as compressive strength in cement mortars. Calcined material, apparently inert, was ground until achieving high finesse. An experimental series made of sugar cane straw ash was introduced, as a reference to the pozzolans previously studied. Ground calcined clays increased its pozzolanic activity at a huge extent, which is characterized by a higher consumption of CH in cement pastes and by a higher compressive strength in cement mortars. Apparently this change takes place due to grinding effect on the reactivity of calcined clayey soils. The best results were obtained from sediment samples before their calcinations. The compressive strength of cement mortars, replacing a 30% the cement weight by such material, is similar to the control (100% cement) at 7 days, and higher at 28 and 60 days. Although such replacement does not decrease total porosity, it does decrease sorptivity, mainly in samples produced with calcined and ground sedimented material. Probably this phenomenon occurs because of pores capillary refining process induced by the precipitation of products of pozzolanic reaction.

Promising technologies for refining ceramic raw materials

It is recommended that efficient refining equipment (Kaskad setup, pulsating setup, electric mass classification apparatus) be used and local unconventional types of raw materials (zeolite- and calcite-containing rock) be drawn into production to obtain from low-grade clays a wide assortment of competitive ceramic wall materials.

Thermal 40Ar/ 39Ar separation of diagenetic from detrital illitic clays in Gulf Coast shales

The 40Ar/ 39Ar age spectra for illite-rich, mixed-layered illite/smectite (I/S) from Texas Gulf Coast bentonites contain only a diagenetic component and are characteristically ‘staircase’-shaped. This spectrum shape contrasts with patterns seen for anchizonal- and epizonal-grade bentonites that are flatter. This may be due to the structural and compositional heterogeneity (mixed layering) typical of low-grade clays, especially with respect to K. On the other hand, shales from depths exceeding those of the smectite-to-illite transformation have both detrital and diagenetic components. Although diagenetic illite-rich I/S dominates shale fine fraction, detrital mica is observed even in the <0.2 μm size fraction. Age spectra of shales consist of two portions: (1) a staircase-shaped low temperature section, corresponding to degassing of the diagenetic illite-rich I/S component, and (2) a peak in the high temperature section, corresponding to degassing of well-crystallized detrital mica. The data obtained from 40Ar/ 39Ar stepwise analysis of these mixtures of diagenetic and detrital components permit at least partial resolution of the diagenetic from the detrital ages. We have developed techniques for quantifying the separate diagenetic and detrital components based on subtraction of the detrital contribution from the age spectrum of mixture, giving rise to an age corrected for the detrital contamination. The resulting corrected 40Ar/ 39Ar ages are closer to the diagenetic ages. This is in sharp contrast to the old K/Ar ages of the same samples. Although still in the developmental state, these techniques appear to represent a solution to the problem of contamination of diagenetic illitic clays by detrital illitic phyllosilicates.

Refinement of low-grade clay by microbial removal of sulfur and iron compounds using Thiobacillus ferrooxidans

The refinement of low-grade clay, of which impurities are mainly sulfur and iron compounds, is required because of the recent shortage of high-grade clay for manufacturing of structural ceramics. The major impurity compound contained in the low-grade clay we treated was identified as pyrite by X-ray powder diffraction and inductively coupled plasma analyses. The well-formed crystals of pyrite had a framboidal form of 1 μm–20 μm diameter. The microbial removal of pyrite from the low-grade clay was investigated by using a sulfur and iron-oxidizing bacterium, Thiobacillus ferrooxidans. About 82–90% of the pyrite was removed in 5–12 d for pulp densities up to 70% (w/v). The removal rate of pyrite ranged from 270 to 914 mg-pyritic sulfur/ l·d depending upon clay pulp density. The rate of pyrite removal (r) could be expressed as a function of pyritic sulfur concentration (S): r (mg-pyritic sulfur/ l·h) = 1.96 × 10 −2 S (mg-pyritic sulfur/ l). The logarithm of the amount of oxidized pyrite per unit volume and the final pH in the reaction medium were found to have a linear relationship which could be expressed as pH = 2.43–0.55 log [FeS 2 (mM)]. With the refined clay no red color due to the presence of pyrite was developed after firing, and its whiteness was similar to that of a high-grade clay.

Use of clay soils in the construction of cutoff curtains

1. In the northwestern region of the country there are numerous clay deposits (more than 150) which belong with respect to chemical composition to hydromica-kaolinite and kaolinite having a low ion-exchange complex and, as a consequence, in a pure form are unsuitable for preparing clay slurries. 2. An improvement of the technological properties of clay slurries from hydromica-kaolinite and kaolinite clays is possible in two main directions: replacement of a certain part of the kaolinite clays (10–20%) by high-grade bentonite clays; increase of the activity of the ion-exchange complex of clays by adding chemical reagents of the group of protective colloids — CMC, TSP, and others. 3. Clay slurries obtained from the low-grade clays of northwestern region have normal technological properties with density ρ=1.15−1.25 g/cm3. At smaller values for density all slurries are characterized by considerable segregation. 4. In all cases when solving the problem of using local clays for preparing thixotropic slurries it is necessary to substantiate the possibility of their use not only on the basis of technical and economic indices but also to take into account the hydrogeological conditions of the objects and technological characteristics of creating a curtain and its design. 5. The use of local clays can considerably broaden the area of use of the slurry trench method for constructing cutoff curtains in the northern and northwestern regions of the country. 6. Experience shows that the maximum use of local materials in hydrotechnical construction of cutoff curtains by the slurry trench method practically always produces a positive effect (1.3–3 rubles/m2).

Beneficiating refractory clays from the Suvorovsk and Ul'yanovsk deposits

We studied the substance composition and developed a technology for the beneficiation of low-grade clays from the Suvorovsk deposits in dense suspensions with the removal from them of pyrites and quartz sands. The beneficiated clay is obtained uniformly, as granules. In chemical composition it corresponds to grades S0 and Sl for refractory raw material from the Suvorovsk deposits.

EFFECT OF ADDING ALUNITE TO REFRACTORY CLAYS

AbstractFour grades of alunite ore were mixed with four grades of fire clays, and the mixtures were formed into modulus of rupture test bars. These were fired to cone 13–14. Specimens were tested for bulk density and modulus of rupture after the initial firing and after reheating to 1400°C. and 1600°C. Softening temperatures of the mixtures were also determined. In general, small quantities (not exceeding 20%) of alunites improved fired characteristics, including decreasing the reheat shrinkage and increasing the P.C.E. The purity of both raw materials was the determining factor. Excessive additions of alunite, particularly to the low‐grade clays, caused bloating as a result of the evolution of sulfur gases from the alunite.