Syrian bean-caper (Zygophyllum fabago L.) improves organic matter and other properties of mine wastes deposits.

The omni-presence of Zygophyllum fabago L. (Syrian bean-caper) natural colonies in post mining areas prompted us to investigate its contributions to reclamation of mine wastes deposits in southeast Spain. Select plant-related (edaphic) characteristics and bio- and water soluble-Cd, Cu, Pb and Zn in rhizosphere of Z. fabago were compared to deposits one year since application of pig slurry and marble waste. Total N in rhizosphere increased up to a factor of 20X (339 vs 17 mg N kg(-1)) in El Gorguel and 27X (85 vs 3.1 mg N kg(-1)) in El Lirio sites. Organic matter accumulation in rhizosphere from litter and roots of Z. fabago increased organic C from 6.6 to 19.5 g kg(-1) in El Gorguel and from 2.1 to 5.7 g kg(-1) in El Lirio in one year. Dissolution of inorganic C takes place due to organic acids from root exudates of Z. fabago. Reduction in bio-available Cd, Cu, Pb, and Zn in rhizosphere of Z. fabago at El Lirio is attributed to increase in pH from 5.3 to 7.7 through marble waste addition, although increased cation exchange capacity may also have played a role. Addition of marble waste to encourage colonization by Z. fabago in acidic mine wastes deposits was recommended.

Marble wastes and pig slurry improve the environmental and plant-relevant properties of mine tailings.

Poor soil fertility is often the biggest challenge to the establishment of vegetation in mine wastes deposits. We conducted field trials in the El Gorguel and El Lirio sites in SE Spain, two representative tailing ponds of similar properties except for pH, to understand the environmental and plant-relevant benefits of marble waste (MW) and pig slurry (PS) applications to mine tailings. Low pH (5.4) tailings (El Lirio) exhibit reduction of up to fourfold in bio-availability of metals as shown by the DTPA-Zn, Pb, water-soluble Zn, Pb and up to 3× for water-soluble Cd. Tailings in El Gorguel have high pH (7.4) and did not exhibit significant trends in the reductions of water-extractable Zn, Pb, Cd and Cu. Improvements to the edaphic (plant-relevant) properties of tailings after the amendments are not as sensitive to pH compared to the environmental characteristics. The two sites had increases in aggregate stability, organic matter (total N and organic C) although total N is higher in the El Gorguel (up to 212 µg N kg(-1)) than the El Lirio (up to 26 µg N kg(-1)). However, cation exchange capacities are similar in both sites at 15.2 cmol(+) kg(-1). We conclude that the characteristics, especially pH, of tailing materials significantly influence the fate of metals but not improvements to plant-relevant properties such as cation exchange capacity and aggregate stability 1 year after the application of MW and PS amendments.