Mineral Inactivation of Zinc in Polluted Soil—Sustainability of Zeolite, Bentonite and Blends

Abstract

The study outlines a novel and traceable procedure for inactivating zinc polluted soil (an Anthrosols) adjacent to a former zinc (Zn) ore mine “Orzel Biały” in Bytom (Poland), where the total content of Zn amounted to 3988.0 mg kg−1. This pollution level initiated an inactivation process involving two natural mineral sorbents, i.e., zeolite (Z) and bentonite (B), as well as their five blends (ZeoBen) expressed as ZB: (1) ZB15/85, (2) ZB30/70, (3) ZB50/50, (4) ZB70/30 and (5) ZB85/15. Next, phosphorus (P) as triple superphosphate (TSP, 46% P2O5) was added to individual ZB at rates: 0.25%, 0.5%, 1.0% and 2.0%. All sorbents were added to the Zn polluted soil at 0%, 0.25%, 0.5%, 1.0% and 2.0% (dry weight basis). Treatments (1.0 kg of Zn-polluted soil with ZB sorbents) were aged for 115 days. Data revealed that ZB85/15 with prevailing zeolite caused a Znact inactivation of 66–71%, while zeolite induced 54% and 47% for bentonite. Reactive zinc (Znreac) decreased much more (20%) when zeolite was incorporated at the rate 2.5 g·kg−1 soil, and bentonite was (10%) at the same rate. The application of the sorbent ZB50/50 enriched with triple superphosphate (TSP) raised the stabilization degree for both Zn fractions. The efficiency was significant at the TSP rate of 2.0% of the sorbent and at least the sorbent +TSP of 10 g·kg−1 soil. The cation exchange capacity (CEC) of about 2 cmol(+)·kg−1 controlled the activity −0.50 mmol·dm−3 of either γZnreac or γZnact, hence a very low zinc ionic activity. The use of mineral blends with higher sharing of zeolite is promising for remediating metal-polluted lands in the case of zinc.

Mineralogical and Physico-Chemical Characterization of the Oraşu-Nou (Romania) Bentonite Resources

“…This study of the Oraşu Nou bentonite reveals a good quality raw material that can be used in many fields of activity: agriculture [22] to immobilize fungicides or insecticides [25], inactivate heavy metals in polluted soils, especially zinc [28], nuclear waste storages [32,33].…”

“…The oriented sample was treated in a closed atmosphere saturated with ethylene glycol vapor for 6 h after which it was analyzed by XRD (Figure 6b). By glycolation, the value of reflex d(001) should increase from 14-15 Å to 17 Å [28,49,50]. The XRD spectra of ethylene glycol saturated-oriented sample from Figure 6b shows the displacement of montmorillonite's the principal peak (001) from 15.93 Å to 17 Å.…”

“…The use of bentonites in environmental protection is reduced when compared to that of natural zeolites. Bentonites mixed with zeolites have been used to inactivate heavy metals in polluted soils, especially zinc [28]. They can also be used in pollutant removal processes for industrial or civilian residual waters [29,30], for the purification of industrial gases, protection of waste storage areas [31], including nuclear waste storages [32,33].…”