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Brazil’s Ministry of Agriculture (Mapa) has formally registered steel slag produced by Companhia Siderúrgica Nacional (CSN) as a fertilizer raw material for soil-acidity correction, opening a new agricultural end-use channel for the steel co-product.
The authorization, issued on Wednesday November 19, follows Mapa’s technical assessment of the material’s chemistry, safety and neutralizing characteristics, enabling nationwide agricultural application.
The approval came two days after a provisionally accepted US field trial reported direct geochemical evidence that steel slag applied to initially acidic soils increased porewater pH and alkalinity, as well as soil pH and calcium saturation.
The authors interpret these changes as indicators of enhanced rock weathering (ERW) under real field conditions.
Mapa’s registration classifies CSN’s aggregate specifically as a raw material to be used in acidity-correcting fertilizer formulations, rather than as a finished fertilizer.
The designation allows the product to be incorporated into agricultural inputs designed to adjust soil pH, expanding CSN’s business beyond traditional markets.
The regulatory approval also follows recent scrutiny of CSN’s historical slag management practices. In early October, federal prosecutors filed an environmental complaint related to legacy slag deposits in Volta Redonda, Rio de Janeiro.
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