New sustainable strategy for rehabilitating phosphate mining sites using phosphate industry by-products and sludge integrating Argan, Carob and Olive trees

In semi-arid context, the development of anthroposol from phosphate industry by-products and sewage sludge could be a new approach for sustainable phosphate mining soils. The objective of this 2 years field study carried out at Benguerir phosphate mine, was to evaluate nutrients and heavy metals dynamics in the soil-plant system of three species planted on anthroposol consisting of a mixture of 65% phosphogypsum (PG), 30% phosphate sludge (PS), and 5% sewage sludge (SS). The experimental layout was a randomized complete block design with six replicates and three species: argan, olive, and carob. No fertilizer was applied to the different plots. Heights and diameters of the different species were measured. Species were pruned, and leaves and stems were separated. The nutrients (N, P, K, Ca, and Mg) and heavy metals (Cd, Cu, Cr, Pb, Ni and Zn) contents in both soil and plant part were determined. The results of the Pearson correlation showed significant correlations between height and diameter of the different species. The strongest correlation was observed for the argan tree. Furthermore, nutrient contents in the rhizosphere of species were significantly reduced, excepted Ca. Also, nutrient contents in leaves were significantly higher than those in the stems. In addition, the concentration of heavy metals in argan, olive and carob leaves, were below international standards. In semi-arid contexts, argan tree could be the best candidate for revegetating mining sites and this anthroposol (65% PG – 30% PS – 5% SS) could be a new approach to rehabilitate mining site on large scale.