Evaluating the effectiveness of sulfidated nano zerovalent iron and sludge co-application for reducing metal mobility in contaminated soil.

Sewage sludge has long been applied to soils as a fertilizer yet may be enriched with leachable metal(loid)s and other pollutants. Sulfidated nanoscale zerovalent iron (S-nZVI) has proven effective at metal sorption; however, risks associated with the use of engineered nanoparticles cannot be neglected. This study investigated the effects of the co-application of composted sewage sludge with S-nZVI for the stabilization of Cd, Pb, Fe, Zn. Five treatments (control, Fe grit, composted sludge, S-nZVI, composted sludge and S-nZVI), two leaching fluids; synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP) fluid were used, samples were incubated at different time intervals of 1 week, 1, 3, and 6 months. Fe grit proved most efficient in reducing the concentration of extractable metals in the batch experiment; the mixture of composted sludge and S-nZVI was the most effective in reducing the leachability of metals in the column systems, while S-nZVI was the most efficient for reducing about 80% of Zn concentration in soil solution. Thus, the combination of two amendments, S-nZVI incorporated with composted sewage sludge and Fe grit proved most effective at reducing metal leaching and possibly lowering the associated risks. Future work should investigate the longer-term efficiency of this combination.

Removal of cadmium in aqueous solutions using a ball milling-assisted one-pot pyrolyzed iron-biochar composite derived from cotton husk.

A novel iron-biochar composite adsorbent was produced via ball milling-assisted one-pot pyrolyzed BM-nZVI-BC 800. Characterization proved that nano zero valent iron was successfully embedded in the newly produced biochar, and the nZVI payload was higher than that of traditional one-pot pyrolyzed methods. BM-nZVI-BC 800 provided a high adsorption performance of cadmium reaching 96.40 mg·g-1 during batch testing. Alkaline conditions were beneficial for cadmium removal of BM-nZVI-BC 800. The pseudo-second-order kinetic model and Langmuir isotherm fitted better, demonstrating that the Cd adsorption on the BM-nZVI-BC 800 was a chemical and surface process. The intraparticle diffusion controlled the adsorption of BM-nZVI-BC 800. The physisorption dominated by high specific surface area and mesoporous structure was the primary mechanism in the removal of cadmium, though electrostatic attraction and complexation also played a secondary role in cadmium adsorption. Compared to adsorbents prepared by more traditional methods, the efficiencies of the ball milling-assisted one-pot pyrolyzed method appears superior.

Cadmium uptake reduction in paddy rice with a combination of water management, soil application of calcium magnesium phosphate and foliar spraying of Si/Se.

A field experiment with 24 different treatments was carried out to study the effects of a combination of water management (WM), soil application of calcium magnesium phosphate (CMP), and foliar spraying of Si/Se on Cd uptake by paddy rice (Teyou 524). The water management modes included W1 (conventional water management) and W2 (flooding during the whole growth period). The application of CMP included P1 (1800 kg·hm-2) and P2 (3000 kg·hm-2). The leaf spraying regulations included LS (2.0 mmol·L-1 Na2SiO3), LX (25 µmol·L-1 Na2SeO3), and LSX (1.0 mmol·L-1 Na2SiO3 and 12.5 µmol·L-1 Na2SeO3). The results indicated that, compared to the control (W1), flooding and CMP reduced soil exchangeable Cd by 10.3, 21.5, 32.2, 27.6 and 36.9% under conditions of W2, P1, P2, W2P1 and W2P2, respectively; but the grain yield was reduced under W2 condition. Some individual treatments, including W2, P1, P2, LS, LX, and LSX, could reduce Cd concentration in the grain by 23.1-60.3%; but the combined regulations could reduce grain Cd concentrations up to 79.5%. Only the combined mode of CMP and leaf spraying of Si/Se could control grain Cd concentration below the Chinese National Food Safety Standard (0.2 mg·kg-1). Combined modes of fertilizer application (W2 and CMP) and foliar spraying (Si/Se), including W2P2LS, W2P2LX, W2P2LSX, were the most effective in reducing the Cd transport coefficients of both root-to-straw (RS) and straw-to-seed (SS). Considering Cd concentration in grain, treatments W2P2LS and W2P2LSX were the most effective ones, which could reduce Cd concentrations to 0.090 mg·kg-1 and 0.089 mg·kg-1 in grain, respectively. These results demonstrated that combined manipulation of the root zone (W2 and CMP) and foliar spraying (Si/Se) can effectively reduce grain Cd concentrations in rice.

The immobilisation and retention of soluble arsenic, cadmium and zinc by biochar.

Water-soluble inorganic pollutants may constitute an environmental toxicity problem if their movement through soils and potential transfer to plants or groundwater is not arrested. The capability of biochar to immobilise and retain arsenic (As), cadmium (Cd) and zinc (Zn) from a multi-element contaminated sediment-derived soil was explored by a column leaching experiment and scanning electron microanalysis (SEM/EDX). Sorption of Cd and Zn to biochar's surfaces assisted a 300 and 45-fold reduction in their leachate concentrations, respectively. Retention of both metals was not affected by considerable leaching of water-soluble carbon from biochar, and could not be reversed following subsequent leaching of the sorbant biochar with water at pH 5.5. Weakly water-soluble As was also retained on biochar's surface but leachate concentrations did not duly decline. It is concluded that biochar can rapidly reduce the mobility of selected contaminants in this polluted soil system, with especially encouraging results for Cd.

Mobility of arsenic, cadmium and zinc in a multi-element contaminated soil profile assessed by in-situ soil pore water sampling, column leaching and sequential extraction.

Three methods for predicting element mobility in soils have been applied to an iron-rich soil, contaminated with arsenic, cadmium and zinc. Soils were collected from 0 to 30 cm, 30 to 70 cm and 70 to 100 cm depths in the field and soil pore water was collected at different depths from an adjacent 100 cm deep trench. Sequential extraction and a column leaching test in the laboratory were compared to element concentrations in pore water sampled directly from the field. Arsenic showed low extractability, low leachability and occurred at low concentrations in pore water samples. Cadmium and zinc were more labile and present in higher concentrations in pore water, increasing with soil depth. Pore water sampling gave the best indication of short term element mobility when field conditions were taken into account, but further extraction and leaching procedures produced a fuller picture of element dynamics, revealing highly labile Cd deep in the soil profile.