Doe Run Peru – Improving productivity with environmental responsibility - Case Study
Doe Run Peru aims to become a preferred global provider of premium metals and services, while at the same time working to operate in a socially and environmentally responsible way. The mining and metals company employs roughly 4,000 people at its operations in Peru’s central Andes. The company has run the La Oroya metallurgical complex since 1997 and the Cobriza mine in the Huancavelica region since 1998. Both were acquired from the Peruvian State.
The La Oroya complex produces premium metals including copper, lead, zinc, bismuth, silver and indium, all important components of state-of-the-art technology, better roadways and improved safety for communities around the world. The underground Cobriza mine, one of the most mechanized mining facility in the country, produces copper concentrates. Cobriza’s sustainable development efforts extend to all of its neighboring communities, especially through community partnerships, with a goal of improving living standards and making direct contributions to development in areas surrounding the company’s facility.
The Metallurgical Complex of La Oroya has been in operation since 1922. Its original owner was The Cerro de Pasco Copper Corp. In 1974 it was expropriated by the Peruvian state and assigned to a state owned enterprise called Centromin Peru. In 1997, it was transferred to Doe Run in a public auction, as part of a larger privatization effort conducted by the Peruvian government.
Doe Run Peru is one of the largest corporations in the Peruvian central Andes. During 2007, Doe Run Peru was the country’s fifth largest exporter, with annual sales of $1.45 billion, acquiring concentrates worth over $1 billion dollars, the overwhelming majority of which are purchased from Peruvian suppliers. The facility sells to markets around the globe, including North and South America, Europe, Asia, Oceania and Africa, as well as the internal Peruvian market.
The smelter and refineries of La Oroya comprise one of the world’s most technically challenging metallurgical facilities, due to the diversity of technologies and operations functioning in one single location for the processing and transformation of polymetallic concentrates into ten refined metals and nine by-products. The complex produces copper, zinc, silver, lead, indium, bismuth, gold, selenium, tellurium and antimony, as well as zinc sulfate, copper sulfate, sulfuric acid, arsenic trioxide, sodium bisulfate, zinc oxide, zinc dust and zinc-silver concentrates.
The facilities at La Oroya include three independent yet totally integrated circuits: zinc, copper, lead and a precious metals sub circuit. Consequently, production at La Oroya consists of many diverse and intricate processes, thanks to the special knowledge and expertise acquired over time.
Since taking over the metallurgical complex of La Oroya, Doe Run Peru has accomplished dramatic, across the board improvements in the environmental performance of the metallurgical complex. This includes a 63-percent reduction in overall dust emissions, 61- percent reduction in lead air levels and the virtual elimination of any polluting impact from the effluents discharged by the metallurgical complex.
As part of it’s dedication to improving environmental conditions, Doe Run recently went online with a $50 million plant to treat sulfur dioxide emissions from the lead circuit of its La Oroya metallurgical complex. The plant, which will help further reduce emissions in La Oroya and lower levels of sulfur dioxide in the mountain community’s air, was inaugurated in late September. Fleck Chemical Industries, Inc. (FCII), responsible for the engineering and design, and Cosapi, general contractor responsible for the field construction of the plant, completed the 15-month project on time.
This Lead Acid Plant was designed to treat up to 58,500 Nm3/h (dry) of hot gas containing 6.3-percent (dry) SO2. Under these conditions the plant will produce 375 tons/day of 98.5-percent sulfuric acid. Alstom supplied the Hot Electrostatic Precipitator and Beltran supplied the Wet Electrostatic Precipitator. The Quench, Venturi scrubbers and gas cooling tower were proprietary designs by FCII.
Given the plant’s high elevation (12,200 ft) and the low SO2 content of the gas, additional cooling of the gas was required to remove sufficient water vapor thus enabling the plant to make a 98.5- percent product. The solution: a shell and tube type condenser located immediately upstream of the dry tower. In the contact and strong acid sections, all the gas/gas heat exchangers and the dry and absorber towers were designed by FCII.
A particularly attractive feature of the contact section was the three-bed stainless steel converter that housed both the hot heat exchanger and the intermediate exchanger. This cost effective design saved gas ducting and valuable space in the very confined area set aside for the acid plant.
Another issue facing the plant installation was the fact that the relatively low temperature used in smelting lead results in the incomplete destruction of organic residues from the flotation process. When these vapors reach the strong sulfuric acid towers they are oxidized to carbon and other constituents. This in turn creates a distinct discoloration of the product acid that renders it less valuable for many applications. FCII’s solution to this concern was to treat this darkened hot acid with a bleaching process that included a hydrogen peroxide solution. The end result is a colorless and more valuable product.
A sodium silicate system was also included in the project to help with the removal of fluorides in the off-gas from the lead sinter machine. These fluorides, if not removed, will slowly erode the domed packing support and other ceramic components in the dry tower. The sodium silicate solution injects a small, metered flow of sodium silicate into the weak acid circulating around the quench tower and the gas cooling tower. The fluorides are readily absorbed by the sodium silicate to form fluorsilisic acid that reacts with the metal ions present in the weak acid to form complex metal fluorides that precipitate out.
The project is the second of three sulfuric acid plants being constructed under the company’s environmental operating agreement with the Peruvian government, known by its Spanish acronym, PAMA.
The first sulfuric acid plant, for the zinc circuit, is already in operation with a capacity of 62,000 metric tons per year. A third plant for the copper circuit is also under construction. The gas cleaning section of this plant, designed by FCII and the contact section, designed by Aker Chemetics, should be completed by October 2009 with an estimated capacity of 200,000 metric tons.
“It has been essential for Doe Run Peru to finish this plant on time as it demonstrates in deeds our commitment and desire to meet our obligations to the Peruvian government and the city of La Oroya,” Juan Carlos Huyhua, Doe Run Peru’s president and general manager, said. Huyhua added that “The fruits of the project’s labor will be seen in an improved quality of life for the people of La Oroya.”