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DEWATERING 54 E&MJ; • OCTOBER 2017 www.e-mj.com Imagine doubling plant throughput from 1,150 metric tons per day (mt/d) to al- most 2,500 mt/d, and perhaps as much as 3,000 mt/d within a reasonable timeframe and at an acceptable cost, all the time working hand in hand with a trustworthy contractor. That would be a plant manag- er's dream. It happened recently in Peru. The oxide plant at the Cerro Pasco oper- ation, which is owned by Volcán Compañía Minera, consists of a series of leaching and metal recovery systems. It had a designed capacity of 2,500 mt/d. Until June 2015, the throughput of the Volcan oxide plant, however, was limited to 1,150 mt/d due to its filtration process. To achieve the de- sired design throughput, engineers decid- ed to upgrade the existing tailings wash- ing stream, a counter current decantation (CCD) circuit, by adding CCD thickeners as fourth and fifth stages to improve the re- covery of the dissolved metals and reduce the cyanide content in the feed to the detox stage, thus increasing metal revenue and decreasing operating costs for the plant. A local firm, Bisa (Buenaventura Inge- nieros S.A.) carried out the full design and engineering of the original Cerro Pasco ox- ide plant. Bisa and Volcán launched a ten- der for the supply of four drum filters, which was awarded to FLSmidth. However, after an initial commissioning and startup phase, the design turned out to be far from optimal as the filters were creating bottlenecks be- cause they were undersized and the design criteria were incorrect. FLSmidth proposed a redesign and replaced the filters with two thickeners instead of the filters. A Breakthrough Solution FLSmidth's Process Engineer Walter Gam- ero described the breakthrough solution implemented at Cerro Pasco's oxide plant. "At the time, the main concerns were the length of the lead times," Gamero said. "To sort this out, pilot testing was performed us- ing paste thickeners to replace the filters." "The testing proved successful and FLSmidth had the gear ready to be sup- plied, so the decision was made to in- stall two paste thickeners," Gamero said. Working under an engineering, procure- ment and construction (EPC) contract val- ued at $10.8 million, the project was fast- tracked and completed in seven months. "The fast track project consideration required a technical office on-site, and from the first day since day Cerro Pas- co and Bisa worked simultaneously with our engineering team, by providing topo- graphic and soil information to complete and release the first package of draw- ings," Gamero said. "This would allow our procurement team to start a bidding pro- cess for the steel fabrication supply, ac- tivity that was part of the critical path. In parallel, the site erection team had to be assembled, recruiting top-notched tech - nically skilled personnel, with the neces- sary capabilities to work safely within a high-risk environment, that included ex- treme altitude and weather conditions." The scope of contract included a com- plete detail engineering; high-level exe- cution plan and technical support for the CCD circuit extension; full procurement, including tanks, agitators, piping bulk, pumps, structural streel bulks, MCC, con- trol system, electrical and instrumenta- tion; bulk materials handling; main plant equipment; construction and pre-com- missioning/commissioning; and advisory on the actual operation for two months. The detail engineering confirmed the outstanding accuracy of the calcula- tions during the proposal stage, allowing FLSmidth to maintain the original speci- fications for the main and ancillary equip- ment prior to procurement. Thickeners Improve Production at Cerro Pasco A Peruvian plant experienced a dramatic increase in capacity through the use of thickeners By Oscar Martinez, Latin American Editor FLSmidth installed two CCD thickeners to replace four filters that were undersized for the mine's oxide plant design.