Electrochemical aspects of grinding media-mineral interactions in magnetite ore grinding

Electrochemical aspects of grinding media-mineral interactions in magnetite ore grinding are illustrated from the viewpoint of corrosive wear of grinding balls and changes in the surface properties of the ground minerals. The corrosive wear of mild steel and HCLA steel was found to be small in contact with magnetite, while the combined presence of pyrrhotite and oxygen accelerated the corrosion of the above ball materials. Austenitic stainless steel exhibited passive behavior under all the above conditions. Galvanic coupling of mild steel with magnetite or pyrrhotite resulted in the formation of a surface reaction product consisting of iron hydroxide species on the mineral.     

Possible solar forcing of 400-year wet–dry climate cycles in northwestern China

Here we present a multi-proxy paleolimnological record from a closed-basin lake (Ebinur Lake) in northwestern China to investigate climate change in this arid region during the last 1,500 years. The 120-cm long sediment core was dated by AMS radiocarbon and ²¹⁰Pb methods. The fine-grained clay sediments contain 3–17% organic matter (OM) and 9–31% carbonate, and are interrupted by multiple sand and silt layers. These sand/silt layers, having consistently low OM, were found at 700–800, 1000–1100, 1300–1400, and 1700–1750 a.d., with a time spacing of 300–400 years. We interpret that the low OM sand/silt layers were deposited during higher lake levels caused by increased river inflow from the surrounding mountains during wet climate intervals. This interpretation is supported by concurrent decreases in δ ¹⁸O and δ ¹³C of bulk carbonate and in carbonate content. Wet climate intervals at 700–800 a.d. and at 1700–1750 a.d. also correlate with elevated snow accumulation and low δ ¹⁸O from Guliya ice core on the NW Tibetan Plateau, both regions strongly influenced by the westerlies. This approximate 400-year periodicity of wet–dry climate oscillations appear to correlate with solar activity as shown by atmosphere ¹⁴C concentration and with paleo-moisture records in interior North America. Our results suggest that solar activities might have played a significant role in driving wet–dry climate oscillations at centennial scales in the interior of Eurasian continent.