Jeong Min Suh

Soil pH Effect on Phosphate Induced Cadmium Precipitation in Arable Soil

The objective of this study was to determine soil pH conditions that allow cadmium (Cd) to precipitate as Cd minerals in phosphate (P) amended soil. Cadmium immobilization could be attributed primarily to Cd adsorption due to increase in pH and negative charge. Soil pH might not affect Cd precipitation as Cd3(PO4)2 by direct reaction of Cd and P in the studied soil, even when soil pH increased up to 9.0. However, Cd might precipitate as CdCO3 with increasing pH up to 9.0 in P untreated soil and up to 8.0 in P treated soil depending on CO2 level.

Comparative Effect of Two Different Types of Phosphate on Cadmium Uptake by Radish (Raphanus sativa L.) Grown in Arable Soil Affected by Mine Activity

To evaluate the effect of type of phosphate (P) material on reducing soil cadmium (Cd) extractability and radish Cd uptake in the field, two different P materials, fused superphosphate (FSP) and dipotassium phosphate (K2HPO4), were applied at rates of 0, 33.5, 100.5, and 167.5 kg P ha−1 before seeding radish (Raphanus sativa L.) in a Cd-contaminated soil. Plant-available Cd concentration in soil and total Cd uptake by radish increased with increasing FSP application but decreased with K2HPO4. The significant decrease in soil pH and negative charge of soil by FSP application led to an increase in bioavailable Cd fraction in soil and in Cd uptake by radish. However, K2HPO4 increased soil pH and negative charge of soil and decreased bioavailable Cd fractions. Soil pH and negative charge of soil played an important role in controlling Cd uptake by radish in soil to which phosphate was applied.

Li+-exchanged Zeolites X and Y (FAU) from Undried Formamide Solution

Two single-crystals of fully dehydrated, partially Li+-exchanged zeolites X (Si/Al = 1.09, crystal 1) and Y (Si/Al = 1.56, crystal 2), were prepared by flow method using 0.1 M LiNO₃ at 393 K for 48 h, respectively, followed by vacuum dehydration at 673 K and 1 × 10 -6 Torr. Their structures were determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3and Fd3m at 100(1) K for crystals 1 and 2, respectively. They were refined to the final error indices R₁/wR₂ = 0.065/0.211 and 0.043/0.169 for crystals 1 and 2, respectively. In crystal 1, about 53 Li+ ions per unit cell are found at three distinct positions; 9 at site I’, 19 at another site I’, and the remaining 25 at site II. The residual 25 Na+ ions occupy three equipoints; 2 are at site I, 7 at site II, and 16 at site III’. In crystal 2, about 31 Li+ ions per unit cell occupy sites I’ and II with occupancies at 22 and 9, respectively; 3, 4, 23, and 3 Na+ ions are found at sites I, I’, II, and III’, respectively. The extent of Li+ ion exchange into zeolite X (crystal 1) is higher than that of zeolite Y (crystal 2), ca. 73% and 56% in crystals 1 and 2, respectively.

Mn(2+)-Ion Site Distribution of Zeolite Y (FAU, Si/Al = 1.56) Depending on the Ion-Exchange Ratio.

To investigate the tendency of Mn(2+)-ion exchange into zeolite Y, four single crystals of fully dehydrated Mn2+, Na(+)-exchanged zeolite Y (Si/Al = 1.56) were prepared by the exchange of Na75-Y (INa75I[Si117Al75,O384]-FAU) with aqueous of various concentrations by Mn2+ and Na+ in a total 0.05 M for molar ratios of 1:1 (crystal 1), 1:25 (crystal 2), 1:50 (crystal 3), and 1:100 (crystal 4), respectively, followed by vacuum dehydration at 400 degrees C. Their single-crystal structures were determined by synchrotron X-ray diffraction techniques in the cubic space group Fd3(-)m and were refined to the final error indices R1/wR2 = 0.0440/0.1545, 0.0369/0.1153, 0.0373/0.1091, and 0.0506/0.1667, respectively. Their unit-cell formulas are approximately LMn33.5Na8I[Si117Al75O384]-FAU, IMn20.5Na34I[Si117Al75O384]-FAU, IMn20.5Na34I[Si117Al75O384]-FAU, and IMn16.5Na42I[Si117Al75O384]-FAU, respectively. The degree of Mn2+-ion exchange increases from 44.3% to 89.1% with increasing the initial Mn2+ concentrations as Na+ content and the unit cell constant of the zeolite framework decrease.