Patent ID: 7691346

Claim:
A method of using lime to raise the pH of a cyanide leach solution used in a heap leach mining operation to recover precious metal values from ore and to thereby produce a recausticized leach solution, the method comprising the steps of: providing a supply of barren cyanide solution from a suitable source; channeling a side stream from the supply of barren cyanide solution to a reactor vessel; encouraging crystal growth within the reactor vessel while introducing a source of lime slurry to the reactor vessel, the lime slurry reacting with contents of the reactor vessel to form a mineral precipitate; initially retaining the mineral precipitate, in the form of particulate solids, within the reactor vessel; pumping overflow from the reactor vessel through a cyclone separation stage which removes particulate solids and creates an overflow stream and an underflow stream; directing the cyclone overflow stream back to the source of barren cyanide solution to upwardly adjust the pH of the bulk of the barren cyanide solution; directing the cyclone underflow stream back to the reactor vessel to thereby provide seed crystal nuclei for precipitate growth within the reactor vessel wherein the cyclone separation stage is accomplished through the use of a hydrocyclone which limits free lime which is discharged in the resulting causticized overflow stream to very fine particles that give a strong increase in pH levels when the causticized stream is mixed with the bulk of the barren cyanide solution; and wherein the pH of the barren cyanide leach solution is adjusted to a pH level that is below calcium hydroxide saturation at a given temperature by combining at least a portion of the cyclone overflow stream with the source of barren cyanide solution, the pH being about 12.45 pH at 25° C.