complex using any suitable technique the ph of a liquid 66 produced by the step 64 is adjusted in a step 68 for example by the addition of lime 70 cao to a value of between 10 and 11 ie to the alkaline operating range of the cyanide leaching step 14 hydrogen cyanide 74 emerging from the step 68 is recycled to the cyanide leaching step 14 the invention provides a number of significant benefits which include the following 1 the nano filtration step 42 effectively removes the high acid consuming free cyanide thereby reducing the amount of sulphuric acid 56 which is subsequently needed to acidify the retentate 2 as the permeate 46 is recycled to the step 14 before the alkalizing step 48 the permeate remains at the correct alkaline ph this reduces the amount of calcium oxide needed to alkalize the liquid 66 and thus to recover the hydrogen cyanide 74 3 due to the decrease in chemical processing a substantial amount of sodium cyanide is recovered in the permeate and is recycled to the step 14 to provide a significant reduction in the reagent 4 the discharge of harmful waste waters in to the environment is reduced the aforementioned benefits produce a substantial saving in operating and capital costs table 2 shows the savings in operating expenditure opex produced by the process according to fig2 when compared to a conventional sart process of the type shown in fig1 fig3 is a flow sheet of a process 10 a which is a modification of.