33 • Significant cost savings due to cement usage reduction • CO₂ emission reduction due to decreased cement use These gains did not compromise technical performance: the CPB met or exceeded UCS targets for stope backfilling (≥ 0.35 MPa) while maintaining the required flowability over transport distances of up to 2 km. This case study demonstrates that with the right chemical technology and process controls, CPB can become a lever for decarbonization and resource efficiency in underground mining. Beyond the technical improvements, this initiative supports Sika’s and Nexa’s ESG commitments and aligns with the global priorities for sustainable development in the mining sector. By transforming tailings from a liability into a structural resource, Cerro Lindo sets a precedent for responsible underground mining in water-stressed, high-impact environments. KEYWORDS Paste Backfill, Cement Reduction, Circular Economy, Sustainability, Cerro Lindo, Nexa Resources, CO₂ Reduction, Water Efficiency, World Mining Congress 1. INTRODUCTION The World Mining Congress 2026 challenges the industry to deliver the minerals the world needs faster, smarter and more responsible, and to build trust with society by changing how mines are designed and operated. Cemented paste backfill (CPB) sits at the intersection of these goals: it enables high ore extraction ratios and stable underground conditions, while offering a route to reuse tailings and reduce the footprint of surface storage facilities. At the same time, CPB often carries a high carbon and water footprint due to its reliance on Portland cement and large volumes of mix water. At Nexa Resources’ Cerro Lindo mine in Peru, CPB is used extensively in sublevel stoping, with two paste plants feeding pipelines up to about 2 km in length. Prior to this work, the backfill system relied on relatively high binder and water contents to guarantee pumpability and meet strength requirements, particularly in long-distance stopes. Against a backdrop of tightening CO₂ and water targets, Nexa and Sika jointly identified CPB optimization as a strategic opportunity to improve sustainability without compromising productivity or safety. 1.1 Scope and objectives The work presented in this paper addresses the WMC 2026 theme by demonstrating how a critical auxiliary process like paste backfill can be engineered to: • Reduce cement and water consumption per cubic meter of paste while maintaining or improving UCS and pumpability; • Increase the proportion of tailings placed underground, thereby reducing surface tailings storage requirements; • Deliver quantifiable water and cement benefits using commercially available materials and existing plant infrastructure;
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