Moisture is one of the important factors influencing mechanical properties of rock. Uniaxial compressive and indirect tensile strengths have been well known to vary from air-dried to water-saturated condition. However, in a uniaxial tension test, which has been difficult to be conducted with a water-saturated rock specimen, knowledge about the effects of moisture is insufficient; for example a complete stress-strain curve has not been obtained. In this study, the uniaxial tensile testing for an air-dried specimen was modified to obtain a complete stress-strain curve for a water-saturated specimen. Especially, bonding method between a specimen and loading platens was carefully reexamined and modified. By the modified testing method, complete stress-strain curves of two andesites, a granite and a tuff were obtained under water-saturated condition. Experimental results under the water saturated condition showed larger inelastic strain at peak strength than that under the air-dried condition. With a two-dimensional specimen model, crack extension in uniaxial tensile test was numerically simulated. Calculated results showed more cracks extension and larger inelastic strain under water-saturated condition as in the experiments.

View full abstract

We reported the rock drillability of rotary-percussion drilling using a roller cone bit in a previous paper. In the present paper, investigation of the rock drillability was extended to percussion drilling using two types of percussion bits. Rocks used for this investigation were granite and two types of andesite having uniaxial compressive strengths of 131 to 214 MPa. Drilling tests were conducted at inlet oil pressures of the percussion drill of 9.5 to 13.5 MPa and at rotary speeds of 25 to 175 rpm. The main results obtained from the tests are as follows:
1. The maximum penetration rate and the minimum specific energy were obtained at the inlet oil pressure of 13.5 MPa, independent of rock and bit types.
2. With respect to the penetration rate and specific energy, the appropriate rotary speed was judged to be about 75 rpm in the high-speed bit and about 100 to 150 rpm in the button bit. In addition, the rotary energy was larger than the percussion energy at the appropriate rotary speed.
3. When rocks were drilled effectively, the effect of the percussion energy and that of the rotary energy on the penetration rate were almost the same.
4. The minimum value of specific energy in percussion drilling using the high-speed bit was correlated very roughly with the uniaxial compressive strength of the rock being drilled.
5. The minimum specific energy of percussion drilling was larger than that of rotary drilling, independent of rock and bit types.

View full abstract

Recently, huge amount of waste has been recycled in cement plant, and many kinds of aversive substances (chlorides, alkalies, sulfates and heavy metal salt) have been brought into cement manufacturing process with the wastes as raw materials. These substances are usually removed by chlorine bypass system from cement kiln-preheater, called as “K powder”. Since cement plant is expected to use more wastes, “K powder” constituents should be separated with each other as recycled resources.
In this study, we tried sulfidized flotation to separate lead components from “K powder” with the recovery of more than 60% by optimizing the flotation conditions, and clarify the reaction mechanism. As a result, we found the optimum conditions in case of 150 g/L pulp density of “K powder” as follows. 1) Adjust the initial pH of the pulp to 3.0 by sulfuric acid, 2) Take 30 min for aging of gypsum formation at the pH 3.0, 3) Add the NaHS of 20 g/kg-“K powder” and take 15 min for sulfidization, 4) Add the PAX of 3.2 g/kg-“K powder” and take 15 min for conditioning, 5) Readjust the pH to 3.0∼4.0 by sulfuric acid and carry out flotation. We also found that the formation of K₂Pb(SO₄)₂ during the conditioning causes the decrease of lead recovery in flotation and that the K₂Pb(SO₄)₂ formation can be suppressed by limiting K⁺ concentration in solution under 800 mmol/L and/or keeping the pulp temperature over 40°C at the stage of NaHS addition. Then, we could separate lead components from “K powder” with the recovery of 60 % as a lead concentration of 10∼30 Pb wt% under the same condition of sulfidized flotation for the “K powders” of various component.

View full abstract

Recently, huge amount of waste has been recycled in cement plant, and many kinds of aversive substances (chlorides, alkalies, sulfates and heavy metal salts) have been brought into cement manufacturing process with the wastes as raw materials. These substances are usually removed by chlorine bypass system from cement kiln-preheater, called as “K powder”. Since cement plant is expected to use more wastes, “K powder” constituents should be separated with each other as recycled resources.
In this study, we tried sulfidized flotation to separate lead components from “K powder” with the recovery of more than 80% by changing the addition order of sulfuric acid and NaHS in flotation conditioning, and also clarify the reaction mechanisms. As a result, we found the optimum conditions of the new process in case of 150 g-“K powder”/L pulp density as follows. 1) Adding NaHS (molar ratio of NaHS/Pb in “K powder”=1.0) into the pulp, and mixing 15 min for sulfidization, 2) Adjusting the pulp pH under 4.0 by sulfuric acid, 3) Mixing the pulp 30-90 min for aging of gypsum formation at pulp pH under 4.0, 4) Adding the total PAX of 1.5 g/kg-“K powder” in 2 or 3 stages, and carrying out 40 min flotation. We also found that the K₂Pb(SO₄)₂ formation which causes the decrease of lead recovery can be suppressed by adding NaHS prior to sulfuric acid addition. Additionally we noted that the new process can decrease the addition of NaHS and PAX to four fifth and half respectively, and can extend the acceptable range of pulp density, gypsum formation pH, gypsum aging time, and flotation pH for good separation compared with the conventional process, then, the process control could become simplified. As the result, we could separate lead components in “K powder” with the recovery over 80 % as a lead concentrate over 40 wt% Pb by this new sulfidized flotation process.

View full abstract

Two bimetallic oxides were formed at 873 K by calcination of hydrotalcite ([(M₁^II_1-xM₂^III_x (OH)₂] (A^n—) _x/n·mH₂O, where M₁ is Mg, M₂ is Al or Fe, A is anionic species, and x is 0<x<1) , for borate and fluoride sorption experiments in aqueous solutions. While the XRD patterns for both bimetallic oxides were assigned to MgO without secondary metallic compounds, SEM-EDX results showed that the secondary metallic elements were evenly distributed on the surfaces of both oxides. When borate and fluoride were sorbed on bimetallic oxides in the Mg—Al system, Al(OH) ₄^— and Mg²⁺ ions were initially released followed by sorption onto the solid phase, but Fe was not released in the bimetallic Mg—Fe oxide system. Regeneration of hydrotalcite was successfully achieved in the Mg—Al system upon borate and fluoride sorption, resulting in greater sorption efficiency with the Mg—Al system as compared to the Mg—Fe system. XPS results for the bimetallic oxides showed that the surface composition was identical to the molar ratio of Al/Mg in the bulk phase of the bimetallic oxide in the Mg—Al system, thus enhancing the regeneration of hydrotalcite.

View full abstract

For a treatment of sewage sludge which contains high levels of chromium, direct melting method of dried sludge has been generally used. The direct melting treatment is usually operated under strong reduction atmosphere not to generate hexavalent chromium. However, hexavalent chromium is not stable under high temperature conditions, so high temperature melting is expected to result in preventing hexavalent chromium generation even not under reduction atmosphere. Heating experiments of sewage sludge were conducted to confirm influences of melting temperature on chromium behavior in slag under oxidation atmosphere. It was confirmed that hexavalent chromium elution from molten slag could be depressed with heating treatment at 1,400°C even under oxidation atmosphere.

View full abstract

A terahertz (THz) wave is an electromagnetic wave with a frequency of appropriately 0.1-100 THz (wave number of 3.3-3333 cm^-1, wavelength of 0.003-3 mm) , at the border between photonics and electronics. For a long time, this frequency range was recognized as the THz gap, owing to the lack of stable sources and detectors of THz waves. Thanks to the recent development of equipment, terahertz technology, which is a combination of technologies using THz waves such as THz photonics, THz electronics, and THz engineering, has been highlighted in many scientific and industrial fields. However, there have been few studies aiming at applying this technology to the field of resource development. In this paper, recent trends in THz technology were reviewed, and the possible application of this technology to resource exploitation, i.e., identification of minerals or substances, was examined. As a result, it was revealed that this technology can be applied for resource exploration, and so further research is warranted in the future.

View full abstract