Abstract: A cobalt recovery method wherein cobalt ions are selectively shifted into an extraction agent mainly composed of either 2-ethyl hexylphosphonate mono-2-ethyl hexylester or di-2 ethyl hexylphosphate in order to extract and separate the cobalt from a solution containing cobalt salts. The method further has a step of stripping the cobalt into an aqueous solution of oxalic acid by bringing the extraction agent containing the cobalt into contact with the aqueous solution of oxalic acid after separation from nickel ion, sodium salt, calcium salt, etc. Cobalt oxalate which does not contain any other salt is then recovered.

Abstract: An inverter apparatus comprises a bridge circuit composed of a combination of a plurality of switching transistors and a microprocessor controlling turning on and turning off of these switching transistors. Patterns of combinations of ON and OFF states of respective switching transistors obtained based on the theory of PWM (pulse width modulation) are stored in a first ROM of microprocessor. Transition of the pattern for each range of 0.degree.-30.degree. in electrical angle is stored in a second ROM in the sequence of periods subdivided from the range. Data of the time during which the pattern to be held for each period is stored in a third ROM. The microprocessor sets the holding time data in a timer, and also outputs the ON/OFF pattern, thereby turning on or turning off of each switching transistor is controlled in accordance with the count of this timer and the ON/OFF pattern. By repeating this cycle, a switching signal which continues during one cycle of AC (range of 0.degree.-360.degree.