Similarly, low malonic acid concentration and prolonged contact time had a negative influence on leaching efficiency. The observation of high leaching efficiency at high malonic acid concentration and prolonged contact time could be because there is a corresponding generation of high amounts of peroxyacetic acid by the excess amount of H2O2 (Equation ) for the leaching of Cu and sufficient contact time for the leaching processes described in Equations 3 -7 to occur respectively. However, at low malonic acid concentration and short contact time low amount of peroxymalonic acid is generated and there is insufficient time for the leaching process leading to low leaching efficiency.