An element of fully aromatic polyamide composite reverse osmosis membrane was taken from a desalination plant after being used for three years, and fouling behavior of the used membrane by Aldrich humic acid was investigated. It was found that the presence of Ca2+ significantly induced water flux decline for both virgin and used membranes. Additionally, compared to virgin membranes, more severe water flux decline was observed for used membranes which are coated with less amount of polyvinyl alcohol. Regarding the rejection of contaminants, the rejection of Cl- and NO3- gradually increased when the feed solution which contains Aldrich humic acid was treated; this trend was not observed for H3BO3. The analysis of experimental data using the solution-diffusion model which allows for the existence of unhindered advection through nano-scale imperfections showed that the increase in the Cl- and NO3- rejection was due to the clogging of nano-scale imperfections by Aldrich humic acid.
Computer simulation of percussive rock drilling requires appropriate numerical models for the interactions among the drill body, rod, rod joint, bit, and rock. In this study, the impact penetration of a bit into rock was investigated for the modeling of the bit-rock interaction. Impact penetration tests on Inada granite were carried out with six rod-bit configurations which were composed of four kinds of button bits and two kinds of rods. In the calculation of force-penetration curves from the measured rod strains, the bit model constructed from the acoustic impedance was simplified, and the empirical data correction method proposed by the authors was applied to all the rod-bit configurations. The force-penetration curves for the six rod-bit configurations showed that the bit force in loading phase was approximately proportional to the square of the penetration. The curves in unloading phase had a linear relation between the bit force and the penetration. The final penetration of each blow had a linear relation with the maximum penetration, and the measured borehole depth was proportional to the maximum penetration. The effect of rod diameter on the force-penetration curves was not obviously observed. On the other hand, the bit force corresponding to the same penetration increased and the specific energy decreased with an increase in bit diameter or in the number of button tips on the bit. These findings will contribute to the improvement of the accuracy in the simulation of percussive rock drilling.
The objective of this study was to investigate the influence of humic substances on the arenate (As(V)) immobilization performance by magnesium oxide (MgO). To achieve the objective, a humic substance-kaoliniteassociate (HSKA) was artificially synthesized as a model for clays containing organic matter and a series of experiments was performed to obtain insights into the behavior of As(V) in HSKA during leaching tests. Our experimental results showed that the influence of humic substances on the As(V) immobilization performance by MgO depended on the type of humic substances. In particular, water-insoluble humin which contains low concentrations of carboxyl and phenol groups had little influence on the As(V) immobilization performance. On the other hand, humic acids which are alkali-soluble and contains relatively high concentrations of these acid functional groups significantly influenced the As(V) immobilization performance, but the way and magnitude of the influence were different depending on the MgO dosage and As(V) content in HSKA. When the MgO dosage was low, humic acids in HSKA positively influenced As(V) immobilization efficiencies by inhibiting soil pH increase and corresponding decrease in the amount of As(V) desorption from HSKA. However, when the MgO dosage was relatively high, humic acids in HSKA negatively influenced As(V) immobilization efficiencies because humic acidsMg2+-As(V) complex were desorbed into the aqueous phase and the complex were poorly sorbed by MgO particles. It was also demonstrated that the magnitude of the influence was larger for the HSKA having lower As(V) content.
In the CERCHAR abrasivity test for rocks, to understand the wear process of styli is important for the appropriate setting of test conditions and for the estimation of bit wear in in-situ rock excavation. In this study, the wear process of a stylus was estimated from both the stylus vertical displacement measured during the test and the groove depth measured after the test. The results showed that the stylus wear during the test can be traced with a simple calculation of the measured values for the two high abrasive rocks, Inada granite and Iwaki sandstone. In those tests, the styli were worn flatly. The calculation was corrected for the other medium to low abrasive eight rocks, because the measured groove depth was not thought to be completely consistent with the penetration depth of the stylus. Comparing the results of the nine rocks with the exception of the granite, the stylus wear continued for longer sliding distance in the tests for higher abrasive rock. It was found from the results of the granite that the mineral constitution affected the wear process of the stylus. In addition, this paper discussed the relation of the CAI (CERCHAR Abrasivity Index) and its variation to the stylus wear process and the rock hardness. On the basis of the results, points of attention in the CERCHAR test were described.