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CELLULAR NEAP LEAC11]NC OF LOV-GRADE GOLD ORES Dy Peul N. Johnson, Ph.D. Hyd rometellurgl eel Engineer 2/10/92 There fa a greet need et this time for a low-grade gold heoD leaching system the[ Ss enrlronnent ally-sate end orcepteble by the puDltc, e(Llc lent In recorering gold end has low ce pltal, operating and enrlronmen[al costs. Recent, more stringent, environmental requirements have made [he old tech- nologies too eapenslre to build and opera [e In most locations. The author be lteres that his "Cal liner Neap Leaching System" (U.S. Paten[ No. 4,526,615)1 is such a system. This sophlstlca[ed heap lase hing system should: • provides very high degree o[ environmental Prot ec [ion to underlying grounduaters rirtuelly forever; • here subs[en[lally lover ce pitel, operating end envlrannental costs then the present technol ogles; • recover between Send 20 De ream[ more gold end use substa ntlally less lime and cyanide reagents then the Dresent tee hnol og/es; • use only a small traction o[ the land eree of [he other tee hnologiea; • canpletely eliminate [I,e need for ell cote rnel leach solution end contaminated rein resereolrs and solution treatment [aciS Sties; • e11n1nate the neeA to sprinkle leach solutl ors on the tops o[ heaps; • use much lee makeup eater; • work yell under cold or vet climatic condi [loos end • signiflcan[ly reduce tl,e capital end ope cat log costs of [he gold recovery Cec111[y. CHARACTER] ST7 CI OF DIFFERENT HEAP LEACH SYSTFJIS Basically, there are three different types o[ heap leaching systems that can De used to leach [rushed ar untrushed gold ores, viz., the "Removable Neap" (RN), the "Pe rmenent Neap' (PH) end the "Cellular Heap" (C11). TIIE RFlIOVABLE NEAP In the Remmra6le Heao method of haan learhlno. rho ,.re +e ..!..-a ,_, _~ ,__ toe crushing plan[, Crushed. stacked on a heart impervious pad to a height of about 10-to-1S feet end leeched by dounuerd percolation of weak cyanide sol utlona for a Derlod of about 20-[0-~5 de ys. The spent m111n{a may [hen be given • eater rinse cycle before being moved [e a tailings vile. -2- The prl nc lpel ed .antege o[ this system 1s the[ 1t ten here a high degree of control end uni [or mitt' over leeching and rinsing, providing that suff lc lent pad eree Ss erslle ble. This meen9 the[ [he maalmue economic recovery (note Figure 1) ten be echl erect with a minimum usage of leaching reagents (I1 me end cyanide). Haue•er, since some ores require long leaching peel ods (uD to 120 days) to reach their meeimun ec onomlc recovery and/or may De slou 1n rlnsing, good vetoes rtes end good rlnsing ere often not et hlered by this means. The principal dl sadrancege of these leeching systems is that they usually here relatlrely hf gh capita] end operating costs. The hea ry Dottom leech pad. stacking eq ulpmen[, the Smpe rriou9 Ded Lor the tailings pile and the tontemineted rein reserroi rs end treatment Estill ties ere high capital cost Items. The removal end disposal oL [el lings and the t vestment of con[eninated refn eaters ere high operating cost steps. In most cases, only higher grade (>0.05 opt Au) ores ha re been treated by this method. THE PERMANENT HEAP In the Permanent Neap method, [he crushed or untrushed ore Is stacked or dumped on a heart' lmpe rrious bottom liner In 10-to-25 foot lifts to a final heap height o[ about 50 feet (untrushed ores are usually stacked 1n mucA taller heaps). Leach solo [l ons are usually spr lnkled on the top surfaces of [he lifts for a IS sect De riod of time and caused to pert ola to dounua rd through the entire underlyl ng pile. The principle advantage of this system is that the ore 15 leached in its f loci repository. Only one moving step is necessary alter crushing. The df sedrante gas o[ this system ere es (ollavs: 1. Their lase hing elflclencles and reagent consumptions are often • vale tl rely Door. This results from orerl caching (the ma:lmun etononlc rec ovary 1s exceeded) Sn the underlying laylra and 1n areas [hat are leeched too long end from underleaching Sn areas uhere the leaching cycle is too shorts Unde rl caching may occur Sn the bottom zones o1 thick lilts that do not get adequate re- agents until late !n the leeching cycle and Sn areas that da not get enough leaching [1 me. Also, reDreciolta tf on of gold relnes may occur In deep heaps or 1n heaps uhere the ores here high reagent consumptions. B11nd spots are another pr o6lem Sn deep hea pa or IS[[s. 2. These heeDS usually have Inrge areal eaten [s. This resin to in high lend, bottom psd end leech solu[f on end ~oncanlneted refn reservoir cosh. J. Voter usage maT 6e high due to eraporetion losses in sprinkll ng.