Experimental study on the fractionation of yttrium from holmium during the coprecipitation with calcium carbonates in seawater solutions

The partitioning of Y and Ho between CaCO3 (calcite and aragonite respectively) and seawater was experimentally investigated at 25 degrees C and I atm. Both Y and Ho were observed to be strongly partitioned into the overgrowths of calcite or aragonite. Their partition coefficients, D-Y and D-Ho, were determined to be similar to 520-1400 and similar to 700-1900 in calcite, similar to 1200-2400 and similar to 2400-4300 in aragonite, respectively. Y fractionates from Ho during the coprecipitation with either calcite or aragonite. Within our experimental conditions, the fractionation factor, k = D-Y/D-Ho, was determined to be similar to 0.62-0.77 in calcite and similar to 0.50-0.57 in aragonite, respectively. The aqueous complexation of Y and Ho, which is a function of solution chemistry, probably plays an important role in both the partitioning and the fractionation. Further analyses suggest that the difference in covalency between Y and Ho associated with changes in their coordination environments is the determinant factor to the Y-Ho fractionation in the H2CO3-CaCO3 System.

黄河源区天然草场的保护与建设

黄河源头地区位于青藏高原东部腹地，地处北纬33°30′～35°40′、东经95°25′～99°25′，海拔高度多在4300～4800m之间，气候具有典型的高原大陆气候的特点。结合20余年来对黄河源区天然草场的调查研究和实践以及对其现状的基本认识，着重分析了自然因素和人为活动引起天然草场变化的途径。结果认为，黄河源区的天然草场虽然有所旱化，但并没有像普遍认为的那样严重，更没有到几近崩溃的边缘，而且这种变化主要是自然因素引起的。最后，针对性地提高了本区天然草场保护、利用、建设和持续发展的措施以及需要深入研究的问题。