Acid-activated Phosphate Rock Research Articles

Stabilization and Ecological Risk Evaluation of Heavy Metals in Farmland Soils by Addition of Attapulgite Modified with Phosphates

Purpose. Attapulgite was modified by sodium dihydrogen phosphate, oxalic acid-activated phosphate rock powder, potassium dihydrogen phosphate, calcium superphosphate, ammonium dihydrogen phosphate, and fused calcium-magnesium phosphate and used in the remediation of Cd, Zn, and Ni. Materials and Methods. Attapulgite was modified by six kinds of phosphate (ratio: 1 : 2), and the improvement effect of passivation material on soil polluted by cadmium, zinc, and nickel was determined. CaCl2-extractable and toxicity characteristic leaching procedure- (TCLP-) extractable Cd, Zn, and Ni were measured in order to estimate the bioavailability and the stabilization efficiency. Pot experiment was conducted to study the enrichment and transport ability of Cd, Zn, and Ni in corn. The ecological risk and ecological toxicity of soil environment were evaluated by calculating SEm, ERIm, CRIm, and BUF. Results and Discussion. Compared with ATP, passivation materials AAPR, AMRP, ASSP, AMAP, and AFMP can improve the stability of CD, Zn, and Ni in soil, and AAPR has the best effect. Compared with CK treatments and ATP treatments, the concentrations of TCLP-extractable Cd decreased by 30.80% and 24.72%, respectively, the concentrations of TCLP-extractable Zn decreased by 15.50% and 11.18%, respectively, and the concentrations of TCLP-extractable Ni decreased by 31.34% and 23.20%, respectively. Compared with ATP treatments, CRI, BUF-Cd, BUF-Ni, and BUF-Zn decreased by 24.67%, 52.88%, 78.73%, and 41.18%, respectively, in the AAPR treatments. Conclusions. Phosphate-modified attapulgite can effectively improve the stability of heavy metals in soil and reduce the migration of heavy metals. In the soil polluted by Cd, Zn, and Ni, the passivation effect of AAPR is the best. Therefore, AAPR can be used as an economical, safe, and effective passivation material to improve Cd-, Zn-, and Ni-contaminated soil, which would have a high utilization value in field applications.

Effect of kaolinite on removal of Pb in simulated wastewater by oxalic acid–activated phosphate rock

Effect of kaolinite on removal of Pb in simulated wastewater by oxalic acid–activated phosphate rock

High-efficiency stabilization of lead in contaminated soil by thermal-organic acid–activated phosphate rock

Phosphate rock powder (PR) has been shown to possess the potential to stabilize lead (Pb) in soil. Most of the phosphorus (P) minerals in the world are low-grade ores, making it difficult to achieve the expected stabilization effect on heavy metals. This study compared the changes in the phase composition and structure of PR and three kinds of activated phosphate rock powder (APR) (organic acid-activated PR, thermal-activated PR, and thermal-organic acid-activated PR). The stabilization effectiveness of APR on Pb-contaminated soil was evaluated by toxicity leaching procedure; the Pb products adsorbed on APR and stabilization mechanism of APR on Pb were analyzed. The results demonstrated that APR showed decreased crystallinity and 3.4-fold increase in specific surface area, and a 53.07% and 49.32% increase in soluble P content in oxalic acid-activated PR and citric acid-activated PR, respectively, when compared with those of PR. These changes improved the stabilization effect of APR on Pb-contaminated soil, in which oxalic acid-600 °C-activated PR showed the best effect, presenting 94.0-99.8% reduction in Pb leaching concentration following addition of 2-10% modifier. Product characterization after Pb adsorption on APR showed that Pb was adsorbed onto APR by forming fluoropyromophite precipitation with APR.

Impacts of oxalic acid-activated phosphate rock and root-induced changes on Pb bioavailability in the rhizosphere and its distribution in mung bean plant.

Rhizosphere acidification in leguminous plants can release P from the dissolution of phosphate compounds which can reduce Pb bioavailability to them via the formation of insoluble Pb compounds in their rhizosphere. A soil polluted from Pb-acid batteries effluent (SPBE), having total Pb=639mgkg-1, was amended with six different rates (0, 0.5, 1, 2, 4 and 6%) of oxalic acid-activated phosphate rock (OAPR) and their effects on pH, available P and bioavailable Pb concentrations in the rhizosphere and bulk soils of mung bean plant were evaluated. Furthermore, the effects of these variant OAPR rates on Pb concentrations in plant parts, bioaccumulation factor (BAF) and translocation factor (TF) for Pb in grain and traits like productivity, the activities of antioxidant enzymes, and grain biochemistry were investigated. Results revealed that increasing rates of OAPR significantly increased pH values and available P while decreased bioavailable Pb concentrations in the rhizosphere over control. The highest dissolution of P in the rhizosphere was with 4 and 6% OAPR rates. As a result, the formation of insoluble Pb compounds affected on reduced Pb concentrations in shoots, roots, and grain in addition to lower grain BAF and TF values for Pb over control. Likewise, the highest plant productivity, improved grain biochemistry, high Ca and Mg concentrations, least oxidative stress, and enhanced soil alkaline phosphatase activity were found with 4 and 6% OAPR rates. The OAPR 4% rate is suggested for reducing grain Pb concentration, cell oxidative injury, and improving grain biochemistry in mung bean.

Feasibility of Stabilized Zn and Pb Contaminated Soils as Roadway Subgrade Materials

The authors have developed a new binder, KMP, which is made from oxalic acid-activated phosphate rock, monopotassium phosphate (KH2PO4), and reactive magnesia (MgO). This study explores the acid neutralization capacity, strength characteristics, water-soaking durability, resilient modulus, and pore size distribution of KMP stabilized soils with individual Zn, Pb, or coexisting Zn and Pb contaminants. For comparison purpose, Portland cement (PC) is also tested. The results show that KMP stabilized soils have a higher acid buffering capacity than PC stabilized soils, regardless of the soil contamination conditions. The water stability coefficient and resilient modulus of the KMP stabilized soils are found to be higher than PC stabilized soils. The reasons for the differences in these properties between KMP and PC stabilized soils are interpreted based on the stability and dissolubility of the main hydration products of the KMP and PC stabilized soils, the soil pore distribution, and concentration of Mg or Ca leached from the KMP and PC stabilized soils obtained from the acid neutralization capacity tests. Overall, this study demonstrates that the KMP is effective in stabilizing soils that are contaminated with Zn or Pb alone and mixed Zn and Pb contaminants, and the KMP stabilized soils are better suited as roadway subgrade material.

Oxalic acid activated phosphate rock and bone meal to immobilize Cu and Pb in mine soils

The contamination of soil by copper (Cu) and lead (Pb) is a serious concern because of its high health risk via the food chain. Oxalic acid-activated phosphate rock (APR) and bone meal (BM) were applied to Cu and Pb co-contaminated soil to investigate their efficacy in the immobilization of Cu and Pb. APR and BM were applied into the contaminated soil (158.8 mg/kg total Pb and 573.2 mg/kg Cu) at four levels of dosages (0.1%, 0.5%, 2%, and 4%) and incubated for one year. The results demonstrated that the acid exchangeable Pb fraction in the soil treated with APR and BM decreased compared to the control, while there was no noticeable change in the acid-exchangeable Cu fraction in the soil treated with either APR or BM. Meanwhile, the application of BM and APR increased the fraction of residual Cu and Pb in the polluted soils. Moreover, the addition of either APR or BM at the dose of 4% decreased the concentrations of CaCl2-extractable Cu and Pb in the amended soil, and the percentages of that reduction in the APR amended soils were 56% and 91% and in BM amended soils were 67% and 64%, respectively. The immobilization of Cu and Pb by APR and BM might be induced by the increased soil pH and soluble P contents in the amended soils. In general, BM is more effective than APR on the immobilization of Cu in polluted soil, while APR had greater efficiency than BM on the immobilization of Pb when the levels of amendments were above 2%.

Remediation of Cd/Ni Contaminated Soil by Biochar and Oxalic Acid Activated Phosphate Rock

Taking soil contaminated with a combination of Cd and Ni as the research objective, biochar, and oxalic acid activated phosphate rock (APR) were applied both together and separately for the remediation of this contaminated soil. The effects of different ratios of amendments on the remediation of Cd and Ni heavy metals in the soil and on inorganic nitrogen and microbial biomass nitrogen (MBN) in the soil were compared. The results show that an increasing amount of biochar and APR, increases the soil pH gradually and acid-extractable Cd and Ni are gradually transformed into reducible, oxidable and residual Cd and Ni, resulting in a reduction in Cd and Ni bioavailability. After 40 days incubation, the acid extractable Ni decreased by 37.04% with a 14.8% increase in residual Ni, and acid extractable Cd decreased 40.28% with a 35.20% increase in residual Cd with the amendment of C50P3 (Applying 50 g·kg-1 biochar and 3 g·kg-1 APR) when compared to C0P0 treatment (Applying nothing). Furthermore, the MBN content for C50P0 (Applying 50 g·kg-1 biochar only) and C0P3 (Applying 3 g·kg-1 APR only) increased by 1.5 and 1 times, respectively, while the content of ammonium nitrogen decreased by 12.5% and 6.4%, respectively and the content of nitrate nitrogen decreased by 11.6% and 10.2%, respectively. This comparison shows that the combined effect of the application of biochar and APR is superior to each respective separate treatment. A mixture of 50 g·kg-1 of biochar and 3g·kg-1 of APR (C50P3) demonstrates the best effect on the remediation of the Cd and Ni in soil. Furthermore, the application of amendments promoted the transformation of inorganic nitrogen into organic nitrogen.

Development of phosphate rock integrated with iron amendment for simultaneous immobilization of Zn and Cr(VI) in an electroplating contaminated soil

This study aims to develop an amendment for simultaneous immobilization of Zn and Cr(VI) in an abandoned electroplating contaminated soil. Nature phosphate rock was first activated with oxalic acid (O-PR) and then combined with FeSO4 or zero-valent iron (ZVI) for immobilization of Zn and Cr(VI) from aqueous solutions. Finally, the optimized approach showing the highest immobilization ability in solution was applied in an electroplating contaminated soil. The O-PR combined with FeSO4 was more effective in simultaneously removing Zn and Cr(VI) than the O-PR integrated with ZVI within the tested solution pH range of 5.5–8.5. Both O-PR with FeSO4 and with ZVI removed over 95% of Zn from the solution; however, only 42–46% of Cr(VI) was immobilized by O-PR with ZVI, while O-PR with FeSO4 almost precipitated all Cr(VI). Moreover, there were 75–95% Zn and 95–100% Cr(VI) remaining in the exhausted O-PR with FeSO4 solid after toxicity characteristic leaching test (TCLP) while the exhausted O-PR with ZVI solid only retained 44–83% Zn and 32–72% Cr(VI). Zinc was immobilized mainly via formation of insoluble Fe-Zn phosphate co-precipitates, while iron-induced reduction of Cr(VI) into stable Cr(OH)3 or CrxFe(1-x)(OH)3 was responsible for Cr(VI) immobilization. Application of the O-PR integrated with FeSO4 in the electroplating contaminated soil rapidly reduced the TCLP extractable Zn and Cr(VI) to below the standard limits, with decrease by 50% and 94%, respectively. This study revealed that combination of oxalic acid activated phosphate rock with FeSO4 could be an effective amendment for remediation of Zn and Cr(VI) contaminated soil.

Influence of phosphorous fertilization on copper phytoextraction and antioxidant defenses in castor bean (Ricinus communis L.).

Application of fertilizers to supply appropriate nutrients has become an essential agricultural strategy for enhancing the efficiency of phytoremediation in heavy metal contaminated soils. The present study was conducted to investigate the beneficial effects of three types of phosphate fertilizers (i.e., oxalic acid-activated phosphate rock (APR), Ca(H2PO4)2, and NaH2PO4) in the range of 0-600mg Pkg-1 soil, on castor bean growth, antioxidants [antioxidative enzymes and glutathione (GSH)], and Cu uptake. Results showed that with the addition of phosphorus fertilizers, the dry weight of castor bean and the Cu concentration in roots increased significantly, resulting in increased Cu extraction. The phosphorus concentration in both shoots and roots was increased as compared with the control, and the Ca(H2PO4)2 treatment had the greatest effect. Application of APR, NaH2PO4, and Ca(H2PO4)2 reduced the malondialdehyde (MDA) content, and the activity of the two antioxidant enzymes superoxide dismustase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6) in the leaves of castor bean. GSH concentration in leaves increased with the increasing levels of phosphorus applied to soil as well as the accumulation of phosphorus in shoots, compared to the control. These results demonstrated that the addition of phosphorus fertilizers can enhance the resistance of castor bean to Cu and increase the Cu extraction efficiency of the plant from contaminated soils.

Chemical immobilization of Pb, Cu, and Cd by phosphate materials and calcium carbonate in contaminated soils.

Soil contamination with toxic metals has increasingly become a global concern over the past few decades. Phosphate and carbonate compounds are good passivation materials for Pb immobilization, while the effect of phosphate and carbonate on the immobilization of multiple heavy metals (Pb, Cu, and Cd) in contaminated soils was seldom investigated. In this study, bone meal (BM), phosphate rock (PR), oxalic acid-activated phosphate rock (APR), super phosphate (SP), and calcium carbonate (CC) were added to the contaminated soils to evaluate the effect of phosphate materials and calcium carbonate on the immobilization of Pb, Cu, and Cd. The results showed that the pH of the treated soils increased 1.3-2.7, except SP which decreased 0.5 at most. Compared to the control treatment, all phosphates and calcium carbonate added to the polluted soils increased the fraction of residual metals, and the application of APR, PR, BM, and CC significantly reduced exchangeable and carbonate-bound fraction metals. PR and APR were the most effective for the immobilization of Pb, Cu, and Cd in the soils among these materials. Moreover, the concentrations of all metals in the toxicity characteristic leaching procedure (TCLP) leachate decreased with increasing amounts of amendments, and the concentrations of Pb in the TCLP leachate for soils treated with PR and APR were below the nonhazardous regulatory limit of 5mgL(-1) (US Environmental Protection Agency). Based on our results, phosphate rock and oxalic acid-activated phosphate rock are effective in the immobilization of multiple metals by reducing their mobility in the co-contaminated soils.

Effect of carbonation on leachability, strength and microstructural characteristics of KMP binder stabilized Zn and Pb contaminated soils

This study presents a systematic investigation of effects of carbonation on the contaminant leachability and unconfined compressive strength of KMP stabilized contaminated soils. A field soil spiked with Zn and Pb individually and together is stabilized using a new KMP additive under standard curing conditions and also with carbonation. The KMP additive is composed of oxalic acid-activated phosphate rock, monopotassium phosphate and reactive magnesia. The stabilized soils are tested for acid neutralization capacity, toxic characteristics leaching characteristics, contaminant speciation and unconfined compression strength. X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy analyses are performed to assess reaction products. The results demonstrate that carbonation increases both acid buffer capacity index and unconfined compressive strength, but decreases leachability of KMP stabilized soils. These results are interpreted based on the changes in chemical speciation of Zn and Pb and also stability and solubility of the reaction products (metal phosphates and carbonates) formed in the soils. Overall, this study demonstrates that carbonation has positive effects on leachability and strength of the KMP stabilized soils.

Immobilization and phytotoxicity of Pb in contaminated soil amended with γ-polyglutamic acid, phosphate rock, and γ-polyglutamic acid-activated phosphate rock.

Pot experiments were conducted to investigate the effects of γ-polyglutamic acid (γ-PGA), phosphate rock (PR), and γ-PGA-activated PR (γ-PGA-PR) on the immobilization and phytotoxicity of Pb in a contaminated soil. The proportion of residual Pb (Re-Pb) in soil was reduced by the addition of γ-PGA but was increased by the application of PR and γ-PGA-PR. The addition of γ-PGA in soil improved the accumulation of Pb in pak choi and decreased the growth of pak choi, suggesting the intensification of Pb phytotoxicity to pak choi. However, opposite effects of PR and γ-PGA-PR on the phytotoxicity of Pb to pak choi in soil were observed. Moreover, in the examined range, γ-PGA-PR activated by a higher amount of γ-PGA resulted in a greater proportion of Re-Pb in soil and weaker phytotoxicity of Pb to pak choi. The predominance of γ-PGA-PR in relieving the phytotoxicity of Pb was ascribed mainly to the increase of soil pH and available phosphate after the amendment, which could facilitate the precipitation of Pb in soil and provide pak choi with more phosphorus nutrient.

New phosphate-based binder for stabilization of soils contaminated with heavy metals: Leaching, strength and microstructure characterization

Cement stabilization is used extensively to remediate soils contaminated with heavy metals. However, previous studies suggest that the elevated zinc (Zn) and lead (Pb) concentrations in the contaminated soils would substantially retard the cement hydration, leading to the deterioration of the performance of cement stabilized soils. This study presents a new binder, KMP, composed of oxalic acid-activated phosphate rock, monopotassium phosphate and reactive magnesia. The effectiveness of stabilization using this binder is investigated on soils spiked with Zn and Pb, individually and together. Several series of tests are conducted including toxicity characteristic leaching (TCLP), ecotoxicity in terms of luminescent bacteria test and unconfined compressive strength. The leachability of a field Zn- and Pb- contaminated soil stabilized with KMP is also evaluated by TCLP leaching test. The results show that the leached Zn concentrations are lower than the China MEP regulatory limit except when Zn and Pb coexist and for the curing time of 7 days. On the other hand, the leached Pb concentrations for stabilized soils with Pb alone or mixed Zn and Pb contamination are much lower than the China MEP or USEPA regulatory limit, irrespective of the curing time. The luminescent bacteria test results show that the toxicity of the stabilized soils has been reduced considerably and is classified as slightly toxic class. The unconfined compressive strength of the soils decrease with the increase in the Zn concentration. The stabilized soils with mixed Zn and Pb contaminants exhibit notably higher leached Zn concentration, while there is lower unconfined compressive strength relative to the soils when contaminated with Zn alone. The X-ray diffraction and scanning electron microscope analyses reveal the presence of bobierrite (Mg3(PO4)2·8H2O) and K-struvite (MgKPO4·6H2O) as the main products formed in the KMP stabilized uncontaminated soils; the formation of hopeite (Zn3(PO4)2·4H2O), scholzite (CaZn2(PO4)2·2H2O), zinc hydroxide (Zn(OH)2), and fluoropyromorphite (Pb5(PO4)3F) in the soils are the main mechanisms for immobilization of Zn and Pb with the KMP binder. The change in the relative quantities of the formed phosphate-based products, with respect to the Zn concentration and presence of mixed Zn and Pb contaminants, can well explain the measured impact of the Zn concentration levels and presence of both Zn and Pb contaminants on the unconfined compressive strength of the KMP stabilized soils.

Immobilization of soil exogenous lead using raw and activated phosphate rocks

Phosphate rock (PR) has been widely and successfully used in immobilization of lead in contaminated soils. However, application of oxalic acid‐activated PR (APR) in the immobilization of lead and particularly investigations about the lead form in the contaminated soils are limited. Exogenous lead (Pb) immobilization was studied by Tessier's sequential extraction procedures after applying raw PRs and oxalic acid APRs into the yellow cinnamon soil (S1) and latosol soil (S2) at four levels of 0 (CK), 50, 500, and 2000 mg P kg−1 soil. The PRs selected were Nanzhang PR (NPR) and Kaiyang PR (KPR), and their activation products were ANPR and AKPR. The results indicated that the content of exchangeable Pb in two soils decreased gradually with the rising PRs amount compared with the control, within 0–7.5 mg kg−1 in S1 and 0–64.1 mg kg−1 in S2. The content of carbonate‐bound Pb changed marginally in S1 while increased substantially in S2 with the increase of PR amount; the change of Fe–Mn oxide‐bound Pb content showed similar change as the carbonate‐bound Pb and organic compound‐bound Pb increased generally. The residue fraction of Pb changed a little for all treatments. To sum up, after applying the testing PRs in two soils, the content of exogenous exchangeable Pb decreased in all treatments and residual fraction augmented conversely in most treatments. Therefore, Pb had been immobilized effectively by PR in thetwo soils and a better fixation effect obtained in APR. ©2013 American Institute of Chemical Engineers Environ Prog, 33: 81–86, 2014