Lithium and rubidium in the Waikato River, New Zealand

Abstract

Abstract Lithium and rubidium in the Waikato River originate partly from geothermal fluids and partly from weathering of surficial volcanic rocks. This paper reports on the distribution and behaviour of these metals in the river system. Total Li concentrations in the river water increased from 0.079 g/m3 at the Lake Taupo outlet to 0.435 g/m3 at Mercer, but the ratios of filtrable to particulate metal decreased from 1.82 to 0.322, respectively. The corresponding concentrations for Rb were 0.038 and 0.626 g/m3, and the ratios were 0.095 and 0.040. Geothermal fluids are the source of about 80% of filtrable Li but only 50% of filtrable Rb. Weathering of volcanic rocks contributes the remainder of the metals. Approximately 11001 each of total Li and total Rb flow annually past Lake Aratiatia and more than 99% of these totals flow into the Tasman Sea. About 3 t of Li and 6 t of Rb accumulate each year into reservoir sediment; reservoir macrophytes, which probably turn over each year, could contain up to 0.5 t ...