Zn In Acidic Soil Research Articles

Chemical fractionation of copper and zinc after addition of carrot pulp biochar and thiourea–modified biochar to a contaminated soil

ABSTRACT In this study, there is presented a thorough investigation of the effect of biochar produced via pyrolysis of carrot pulp with pre and post-modification by thiourea (CH4N2S) at three rates (0, 4%, and 8%) on fractionation of Cu and Zn in acidic soil. The sequential extraction procedure of BCR was utilized for the determination of heavy metals fractionation. According to the FTIR analysis, the thiourea-modified biochar (TMB) had more surface functional groups in comparison with the carrot pulp biochar (CB). The 8% TMB application, was more effective in increasing the CEC, pH, EC, and SOC of the soil than the 8% CB treatment. The BCR test revealed that after the addition of CB and TMB, the acid extractable Cu and Zn decreased considerably. Thiourea-modified biochar was more effective than pristine biochar in decreasing the acid extractable metals fraction. The addition of TMB induced the conversion of the acid extractable fraction of Cu to residual and organic matter bound fractions, and the acid extractable fraction of Zn to residual, organic matter bound and oxides bound fractions. This work suggests that thiourea-modified biochar can be a low-cost and effective amendment for immobilizing Cu and Zn in contaminated acidic soils.

Simultaneous sorption and desorption of Cd, Cr, Cu, Ni, Pb, and Zn in acid soils: I. Selectivity sequences

The sorption and desorption of six heavy metals by and from the surface or immediately subsurface horizons of eleven acid soils of Galicia (N.W. Spain) were characterized by means of batch experiments in which the initial sorption solution contained identical mass concentrations of each metal. Concentration-dependent coefficients K d were calculated for the distribution of the metals between the soil and solution phases, and the values obtained for initial sorption solution concentrations of 100 mg L −1 of each metal ( K d100) were used, for each soil, to order the metals as regards their sorption and retention. Pb and Cu were sorbed and retained to a greater extent than Cd, Ni or Zn, which had low K d100 values. Pb was sorbed more than any other metal. Cr was generally sorbed only slightly more than Cd, Ni or Zn, but was strongly retained, with K d100 (retention) values greater than those of Pb and Cu in soils with very low CEC (<3 cmol (+) kg −1). The sorption of Pb and Cu correlated with organic matter content, while the retention of these and the other metals considered appeared to depend on clay minerals, especially kaolinite, gibbsite, and vermiculite.

Simultaneous sorption and desorption of Cd, Cr, Cu, Ni, Pb, and Zn in acid soils: II. Soil ranking and influence of soil characteristics

In Part I of this paper we reported, for each of 11 acid soils, the rankings of six metals according to their sorption from solutions containing all six, and according to their retention under desorption conditions. Here, we analyse the same data from a different perspective: for each metal, we rank the soils by their capacities to sorb and retain it as reflected by soil/solution distribution coefficients K d100 measured using starting solutions containing 100 mg L −1 of each metal. We also ranked the soils for overall heavy metal sorption and retention capacities using Kaplan's compound measure K dΣ, and we investigated the influence of soil characteristics on K d100 and K dΣ100 values. Overall capacity for sorption of heavy metals was positively related to HOM, kaolinite and Fe oxides contents, and negatively related to CEC and to vermiculite and haematite contents. Overall capacity for retention of heavy metals was positively related to HOM and kaolinite contents, and negatively related to CEC and vermiculite content. The good correlation between K dΣ100(sorption) and the first component extracted in a principal components analysis of K d100(sorption) values, and between K dΣ100(retention) and the first component extracted in a principal components analysis of K d100(retention) values, supports the adequacy of K dΣ as a measure of the overall capacity of a soil to sorb or retain heavy metals.

Effect of Ammonium, Potassium, and Sodium Cations and Phosphate, Nitrate, and Chloride Anions on Zinc Sorption and Lability in Selected Acid and Calcareous Soils

Zinc availability and mobility in soils is controlled by its interaction with the soil matrix and amendments. Contradicting evidence has been reported for factors influencing Zn behavior in soils. This study was conducted to investigate the effect of common cations and anions on Zn sorption and lability characteristics. Zinc sorption isotherms were conducted on three acid and four calcareous soils in NH4+, K+, and Na+ and H2PO4−, NO3− and Cl− backgrounds. Lability of the sorbed Zn was evaluated by DTPA following sorption. Calcareous soils exhibited greater Zn sorption than did acid soils. Predicted Langmuir maxima for Zn sorption differed among the various ionic backgrounds. A majority of the total sorbed Zn (60–96%) was recoverable in the labile fraction. Both NH4+ and K+ equally decreased Zn sorption, as opposed to Na+ in acid and calcareous soils; however NH4+ yielded 4 to 12% more of sorbed Zn into the labile pool than did K+ in acid soils. Zinc sorption was enhanced by H2PO4− as opposed to Cl− or NO3− in acid soils, but it was decreased in three out of four calcareous soils. The effect of H2PO4− on the lability of the sorbed Zn in acid soils was similar to that of Cl− or NO3−, but in calcareous soils the phosphate held 10‐25% more of the sorbed Zn in the nonlabile pool. It was concluded that even in calcareous soils, total Zn sorption could be impacted by phosphate–Fe oxide interactions. Furthermore, the effect of background ions on the lability of sorbed Zn varied between acid and calcareous soils. These results have important implications on Zn management in relation to other nutrients.

SORPTION OF ZINC ON IRON HYDROUS OXIDE

We studied the sorption reactions of zinc (Zn) with freshly prepared hydrous iron oxide gels modified to provide phosphorus/iron (P/Fe) ratios of 0, 0.05, 0.10, 0.20, and 0.40. Hydrous oxides have a high adsorptive capacity for Zn in acid soils and soils affected by submergence. Zinc concentrations from 0 to 10 mg/L were used to evaluate sorption phenomena where P and Zn interact to affect Zn solution concentration. Sorbed P tends to lower the ZPC of the oxides and increases the net negative charge on its surfaces. The pH of the media affects solution Zn-P-Fe relationships, because the surface charge on the oxide is pH-dependent. This study concludes that hydrous iron oxides may play an important role in the sorption of Zn in soils and possibly affect its availability to crops.