GENERAL47956 - Laserfiche WebLink

Home Browse Search

Pape 3 hlph vdumes of low pressure air. In this application a reduction In total cyankJe of 92 percent was achieved by lowering the cyanke concentration from 560 mg fl to 44 mg/I. - . -' The mayor problem associated with the system was the buildup of gypsum and copper thlocyanate precipitates on the packing intemals, which required manually deaning every two to tour months. The problem arose due lb the very low pH Lind h(gti sulfate concentrations generated, two probems minimized In modern adaptations of the process. The process was utilized for economic, not environmental reasons) and was IlmBed to the stripping of cyande'from clarKied barren soutions, ~ slurries. During the 7930'sr ~ there were about seven cyanide regeneration plants In operation utilizing various designs, bit only limited Information was available concerning these facilities (4). The plants were utilized in conjunction with silver recovery primarily and were located In remote regions of the world. From the mid-1930'5 Into the 1950'5, afull-scale cyanide regeneration or recovery process was utilized by the Real Del Monte Company In Pachuca, Hidalgo, Mexico (5). The stripping of free cyanide was conducted at an acidic pH, employing sulfuric acid generated on-site through the burning of sulfur. The volatilization stage and absorber stages were combined alternately and operated In series. The system was enclosed and the air recycled at t00 percent humidity to minimize evaporation. A total cyanide recovery of about 93 percent was achieved with about a 60 percent removal realized through each of the three stepper stages. The operation was originally designed to treat about 350 tonnes o1 solution per day and was Ia.er expanded to accommodate about 1,100 tonnes of solution per day. The free cyanide was concentrated until a 5 percent sdution was obtained and then recycled to the metallurgical circuit. However, the process was restricted to recovery of cyanide from clarified barren solutions only. In the 7970'5 the process was reinvestigated and modernized by CANMET and McNamara (6). The renewed interest fn the process was due to the increasing costs of both cyanide and its treatment. In .he CANMEf study, abench-scale laboratory apparatus was employed to Investigate the recovery of cyanide from sot actual barren waters. The study summarized for the first time the various chemical reactions as:>ociated with the process. The process was referred to as aclditication, voaatilization, and reneutralization or the AVR process, which Is the current terminology for cyanide recovery and regeneration from soluticns. The study advocated the use of single complete mix aeration basins about 1.Sm in depth instea~f of stripping towers, to minimize the mechanical problems associated with scaling and plugging of media or internals, ;' and to minimize pressure drop and horsepower requirements. It was recommended that aeration in a full- ~ ~ scale operation be accomplished using multiple rows of fine bubble diffusers. The AVR process was evaluated as a primary wastewater treatment alternative. utilizin0 pH values below 2.0 to facilitate removal of total and iron comolexed-GyanidES_ittcouglLp~ci nation; Greater thait~-,(1,ercent ~~ ._. ~ ~` -removal ota~}ranide was achieved In the studies, with treated etttuents containing total cyanides ranging ~.. _ - fr 0.70 to 4.0 mg In addition, the Investigation of metals precipitation was Undertaken, demonstrating _ _ =: - ` excellent remova efficiencies were achievable following reneutraliiation with lime. However, the process _;. , . was confined to sQlttliotLtteaicent as it was considered not feasible.(or.t[eatment,of-tailings slurries. In '~ addition, the use of basins and fine bubble diffusers Increased the horsepower requirements t:ompared to towers, due to the Increased pressure fosses encountered In the system. The AVR process was further Investigated as a primary alternative for treatment of mine decant water from I 'L 7985-7987 (Madder, unpublished results). The tests employed a small pilot plant operated In batch mode using barren waters obtained from a silver mining operation. The pilot plant design Involved two 0.3m diameter 2.5m pdyethytene columns connected In series. One cdumn served as the stripping chamber, while the other served as the absorption chart,ber. About 200 L of actual decant solution were utilized per experiment In conjunction with coarse bubble diffusers, as h was found turbulence was a more Important factor In stripping of cyanide than the size of the bubble. The