Stabilization of lead (Pb) and zinc (Zn) in contaminated rice paddy soil using starfish: A preliminary study.

Lead (Pb) and zinc (Zn) contaminated rice paddy soil was stabilized using natural (NSF) and calcined starfish (CSF). Contaminated soil was treated with NSF in the range of 0-10 wt% and CSF in the range of 0-5 wt% and cured for 28 days. Toxicity characteristic leaching procedure (TCLP) test was used to evaluate effectiveness of starfish treatment. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) analyses were conducted to investigate the mechanism responsible for effective immobilization of Pb and Zn. Experimental results suggest that NSF and CSF treatments effectively immobilize Pb and Zn in treated rice paddy soil. TCLP levels for Pb and Zn were reduced with increasing NSF and CSF dosage. Comparison of the two treatment methods reveals that CSF treatment is more effective than NSF treatment. Leachability of the two metals is reduced approximately 58% for Pb and 51% for Zn, upon 10 wt% NSF treatment. More pronounced leachability reductions, 93% for Pb and 76% for Zn, are achieved upon treatment with 5 wt% CSF. Sequential extraction results reveal that NSF and CSF treatments of contaminated soil generated decrease in exchangeable/weak acid Pb and Zn soluble fractions, and increase of residual Pb and Zn fractions. Results for the SEM-EDX sample treated with 5 wt% CSF indicate that effective Pb and Zn immobilization is most probably associated with calcium silicate hydrates (CSHs) and calcium aluminum hydrates (CAHs).

Quality improvement of acidic soils by biochar derived from renewable materials.

Biochar derived from waste plant materials and agricultural residues was used to improve the quality of an acidic soil. The acidic soil was treated for 1 month with both soy bean stover-derived biochar and oak-derived biochar in the range of 1 to 5 wt% for pH improvement and exchangeable cation enhancement. Following 1 month of treatment, the soil pH was monitored and exchangeable cations were measured. Moreover, a maize growth experiment was performed for 14 days with selected treated soil samples to confirm the effectiveness of the treatment. The results showed that the pH of the treated acidic soil increased by more than 2 units, and the exchangeable cation values were greatly enhanced upon treatment with 5 wt% of both biochars, after 1 month of curing. Maize growth was superior in the 3 wt% biochar-treated samples compared to the control sample. The presented results demonstrate the effective use of biochar derived from renewable materials such as waste plant materials and agricultural residues for quality improvement of acidic soils.

Assessment of waste oyster shells and coal mine drainage sludge for the stabilization of As-, Pb-, and Cu-contaminated soil.

A novel treatment mix was designed for the simultaneous immobilization of As, Cu, and Pb in contaminated soils using natural (waste oyster shells (WOS)) and industrial (coal mine drainage sludge (CMDS)) waste materials. The treatments were conducted using the standard U.S. sieve size no. 20 (0.85 mm) calcined oyster shells (COS) and CMDS materials with a curing time of 1 and 28 days. The As immobilization treatments were evaluated using the 1-N HCl extraction fluid, whereas the Pb and Cu immobilization treatments were evaluated using the 0.1-N HCl extraction fluid based on the Korean leaching standards. The treatment results showed that the immobilization of As, Cu, and Pb was best achieved using a combination mix of 10 wt% COS and 10 wt% CMDS. This treatment mix was highly effective leading to superior leachability reductions for all three target contaminants (>93 % for As and >99 % for Cu and Pb) for a curing period of 28 days. The X-ray absorption near-edge structure (XANES) results showed that As was present in the form of As(V) in the control sample and that no changes in As speciation were observed following the COS-CMDS treatments. The scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) sample treated with 10 wt% COS and 10 wt% CMDS indicated that As immobilization may be associated with the formation of Ca-As and Fe-As precipitates while Pb and Cu immobilization was most probably linked to calcium silicate hydrates (CSHs) and calcium aluminum hydrates (CAHs).

Stabilization of As-, Pb-, and Cu-contaminated soil using calcined oyster shells and steel slag.

In this study, As-, Pb-, and Cu-contaminated soil was stabilized using calcined oyster shells (COS) and steel slag (SS). The As-contaminated soil was obtained from a timber mill site where chromate copper arsenate (CCA) was used as a preservative. On the other hand, Pb- and Cu-contaminated soil was obtained from a firing range. These two soils were thoroughly mixed to represent As-, Pb-, and Cu-contaminated soil. Calcined oyster shells were obtained by treating waste oyster shells at a high temperature using the calcination process. The effectiveness of stabilization was evaluated by 1-N HCl extraction for As and 0.1-N HCl extraction for Pb and Cu. The treatment results showed that As, Pb, and Cu leachability were significantly reduced upon the combination treatment of COS and SS. The sole treatment of SS (10 wt%) did not show effective stabilization. However, the combination treatment of COS and SS showed a significant reduction in As, Pb, and Cu leachability. The best stabilization results were obtained from the combination treatment of 15 wt% COS and 10 wt% SS. The SEM-EDX results suggested that the effective stabilization of As was most probably achieved by the formation of Ca-As and Fe-As precipitates. In the case of Pb and Cu, stabilization was most probably associated with the formation of pozzolanic reaction products such as CSHs and CAHs.

Soil washing of fluorine contaminated soil using various washing solutions.

Bench-scale soil washing experiments were conducted to remove fluoride from contaminated soils. Five washing solutions including hydrochloric acid (HCl), nitric acid (HNO3), sodium hydroxide (NaOH), sulfuric acid (H2SO4) and tartaric acid (C4H6O6) were tested. The concentration of the washing solutions used ranged from 0.1 to 3 M with a liquid to solid ratio of 10. The soil washing results showed that the most effective washing solution for the removal of fluoride from contaminated soils was HCl. The highest fluoride removal results of approximately 97 % from the contaminated soil were obtained using 3 M HCl. The fluoride removal efficiency of the washing solution increases in the following order: C4H6O6 < NaOH < H2SO4 < HNO3 < HCl.

Evaluation of ettringite-related swelling mechanisms for treated chromite ore processing residue.

Accelerated one-dimensional unconfined swell tests were conducted for ferrous sulfate chromite ore processing residue (COPR) field-treated samples. The field-treated samples were subjected to wet and dry cycles over 100 days to accelerate the lithification of the samples. Parallel laboratory experiments were performed to investigate the effects of mineralogy on COPR swell under controlled conditions. The field and laboratory samples were treated with ferrous sulfate at a ferrous-to-Cr(6+) molar stoichiometric ratios of eight (8×) and five (5×). X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) analyses were used to investigate the mineralogical changes upon treatment. The swell results indicated that significant COPR swelling was observed in all of the tested samples. The swelling was more pronounced in the 5× treated COPR sample than in the 8× treated COPR sample. Moreover, the laboratory-treated samples showed greater swelling behavior as compared with the field-treated samples, which was most probably due to the high dry density of the COPR, indicating that dry density was a more dominant factor than lithification. XRPD and SEM-EDX results confirmed that significant ettringite formation occurred in all treated samples.

Assessment of natural and calcined starfish for the amelioration of acidic soil.

Quality improvement of acidic soil (with an initial pH of approximately 4.5) with respect to soil pH, exchangeable cations, organic matter content, and maize growth was attempted using natural (NSF) and calcined starfish (CSF). Acidic soil was amended with NSF and CSF in the range of 1 to 10 wt.% to improve soil pH, organic matter content, and exchangeable cations. Following the treatment, the soil pH was monitored for periods up to 3 months. The exchangeable cations were measured after 1 month of curing. After a curing period of 1 month, the maize growth experiment was performed with selected treated samples to evaluate the effectiveness of the treatment. The results show that 1 wt.% of NSF and CSF (700 and 900 °C) were required to increase the soil pH to a value higher than 7. In the case of CSF (900 °C), 1 wt.% was sufficient to increase the soil pH value to 9 due to the strong alkalinity in the treatment. No significant changes in soil pHs were observed after 7 days of curing and up to 3 months of curing. Upon treatment, the cation exchange capacity values significantly increased as compared to the untreated samples. The organic content of the samples increased upon NSF treatment, but it remains virtually unchanged upon CSF treatment. Maize growth was greater in the treated samples rather than the untreated samples, except for the samples treated with 1 and 3 wt.% CSF (900 °C), where maize growth was limited due to strong alkalinity. This indicates that the amelioration of acidic soil using natural and calcined starfish is beneficial for plant growth as long as the application rate does not produce alkaline conditions outside the optimal pH range for maize growth.

Amelioration of acidic soil using various renewable waste resources.

In this study, improvement of acidic soil with respect to soil pH and exchangeable cations was attempted for sample with an initial pH of approximately 5. Acidic soil was amended with various waste resources in the range of 1 to 5 wt.% including waste oyster shells (WOS), calcined oyster shells (COS), Class C fly ash (FA), and cement kiln dust (CKD) to improve soil pH and exchangeable cations. Upon treatment, the soil pH was monitored for periods up to 3 months. The exchangeable cations were measured after 1 month of curing. After a curing period of 1 month, a maize growth experiment was conducted with selected-treated samples to evaluate the effectiveness of treatment. The treatment results indicate that in order to increase the soil pH to a value of 7, 1 wt.% of WOS, 3 wt.% of FA, and 1 wt.% of CKD are required. In the case of COS, 1 wt.% was more than enough to increase the soil pH value to 7 because of COS's strong alkalinity. Moreover, the soil pH increases after a curing period of 7 days and remains virtually unchanged thereafter up to 1 month of curing. Upon treatment, the summation of cations (Ca, Mg, K, and Na) significantly increased. The growth of maize is superior in the treated samples rather than the untreated one, indicating that the amelioration of acidic soil is beneficial to plant growth, since soil pH was improved and nutrients were replenished.

Stabilization of lead and copper contaminated firing range soil using calcined oyster shells and fly ash.

A stabilization/solidification treatment scheme was devised to stabilize Pb and Cu contaminated soil from a firing range using renewable waste resources as additives, namely waste oyster shells (WOS) and fly ash (FA). The WOS, serving as the primary stabilizing agent, was pre-treated at a high temperature to activate quicklime from calcite. Class C FA was used as a secondary additive along with the calcined oyster shells (COS). The effectiveness of the treatment was evaluated by means of the toxicity characteristic leaching procedure (TCLP) and the 0.1 M HCl extraction tests following a curing period of 28 days. The combined treatment with 10 wt% COS and 5 wt% FA cause a significant reduction in Pb (>98 %) and Cu (>96 %) leachability which was indicated by the results from both extraction tests (TCLP and 0.1 M HCl). Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) analyses are used to investigate the mechanism responsible for Pb and Cu stabilization. SEM-EDX results indicate that effective Pb and Cu immobilization using the combined COS-FA treatment is most probably associated with ettringite and pozzolanic reaction products. The treatment results suggest that the combined COS-FA treatment is a cost effective method for the stabilization of firing range soil.

Stabilization of Pb²âº and Cu²âº contaminated firing range soil using calcined oyster shells and waste cow bones.

Pb(2+) and Cu(2+) contamination at army firing ranges poses serious environmental and health risks to nearby communities necessitating an immediate and prompt remedial action. In this study, a novel mixture of calcined oyster shells (COSs) and waste cow bones (WCBs) was utilized to immobilize Pb(2+) and Cu(2+) in army firing range soils. The effectiveness of the treatment was evaluated based on the Korean Standard leaching test. The treatment results showed that Pb(2+) and Cu(2+) immobilization in the army firing range soil was effective in significantly reducing Pb(2+) and Cu(2+) leachability upon the combined treatment with COS and WCB. A drastic reduction in Pb(2+) (99%) and Cu(2+) leachability (95%) was obtained as compared to the control sample, upon treatment with 5 wt.% COS and 5 wt.% WCB. The combination treatment of COS and WCB was more effective for Pb immobilization, than the treatment with COS or WCB alone. The 5 wt.% COS alone treatment resulted in 95% reduction in Cu(2+) leachability. The SEM-EDX results suggested that Pb(2+) and Cu(2+) immobilization was most probably associated with the formation of ettringite, pozzolanic reaction products and pyromorphite-like phases at the same time.

Stabilization of Cu-contaminated army firing range soils using waste oyster shells.

stabilization/solidification (S/S) process was used to immobilize Cu in contaminated soils obtained from two army firing ranges sites (A and B) with total Cu concentrations of 520 and 380 mg/kg, respectively. Both waste oyster shells (WOS) and pretreated oyster shells (POS) were used to immobilize Cu in the contaminated soils. Waste oyster shells passing the #10 mesh and #20 mesh were used for the Sites A and B, respectively. WOS- and POS-treated soil samples cured for 28 days were evaluated for Cu leaching by the Korean Standard Leaching Test (KSLT) method. Slurry suspensions were prepared to investigate the Cu immobilization mechanism using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) energy dispersive X-ray spectroscopy (EDX) analyses. The treatment results showed that the POS treatment was more effective than the WOS treatment of 28 days. For Site A, 10 wt% WOS and 3 wt% POS dosages were required to pass the Korean warning standard of 50 mg/kg, while 10 wt% WOS and 5 wt% POS dosages were required for the Site B treatment. The XRPD and SEM-EDX results showed that Cu immobilization was strongly linked to both CSH/CAH and ettringite. Overall, the POS treatment was effective at immobilizing the Cu in the contaminated soils, very likely due to its CaO content.