972 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; • Showcase a collaborative innovation model between a mining company and a technology provider, focusing on documented engineering contributions rather than promotion of specific products. The scope covers tailings characterization, state-of-the-art review, laboratory mix design, industrial trial implementation and interpretation of technical, sustainability and economic results. 2. BACKGROUND AND STATE OF THE ART 2.1 Cemented Paste Backfill and sustainability CPB is widely used to backfill underground voids with a mixture of dewatered tailings, water and hydraulic binders, providing ground support and allowing higher extraction ratios. Numerous studies have shown that CPB helps reduce the area, volume and risk of surface tailings impoundments and can improve overall mine stability and safety. At the same time, life-cycle assessments identify cement use in backfill as a major contributor to embedded greenhouse gas emissions due to the energy-intensive clinker production process. Optimizing binder content without compromising strength is therefore a key decarbonization lever. Recent research and field practice have highlighted three main avenues for more sustainable CPB: (i) optimizing mix design to reduce cement and water demand; (ii) partially replacing Portland cement with alternative binders or supplementary cementitious materials; and (iii) using chemical admixtures to decouple rheology from water content, enabling higher solids contents and lower water-to-cement ratios while maintaining pumpability and stability.
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