| The heavy metal pollution, such as cadmium, has been attracted mone and more attention in south area of China. Not only do heavy metal pollutions seriously restrict the agricultural production but also threaten safety of agricultural products. According to reports more than one third of cultivated soil was contaminated by cadmium and environment incident happen frequently, especially for the events of "Cd rice" which happened in Hunan province in 2011 and 2013, striking on trading markets heavily and impacting on the stability of society. It is unwise to cease all the agriculture production processing on soil mildly contaminated by heavy metal of Cd or to transfer into the non-agriculture plough, considering to the current situation of less ground for more civilians. So it makes great sense to developing in situ immobilization technology of heavy metal, realizing restoring and producing side by side.The nano-adsorbent possess of strong adsorption fixation effect to heavy metal cadmium, indicating the potential application of value of adsorbent to in situ immobilization of cadmium in soil. Whereas considering the blemish to property of nano-materials of unstable surface structure, agglomeration and easy interference in environment, it can not work very well in utility of practice. One alternative method is to support nano materials onto the organic polymer displaying high water adsorption ability, in that way not only to solve the problem of easy aggregation of nano-adsorbents in soil but also to prevent macromolecule organic matter and clay mineral from interfering the adsorption immobilization of calcium in soil.In this paper, a method known as copolymerization synthesis is introduced, in summary, the cation exchange resin:poly(acrylamide-co-sodium acrylate) (PP) loading nano size manganese hydroxide (MO), is made into organic-inorganic composite (PPM). The Infrared Spectral Analysis (FTIR), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and other characteristic methods of material were conducted for analysis on the structure and mechanism of material absorption. Meanwhile the study on the effects of pH, time, competitive cations and other factors to the adsorption of cadmium by material were also conducted. TEM revealed the mostly MO nanoparticles with size of 5-20 nm were dispersed in polymer. The adsorption experiments indicated that removal of cadmium in solution can be increased significantly with PP loading some amount of MO (1.05%), the adsorption capacity of cadmium with PPM reached 507.98 mg/g, while with PP reached 281.19 mg/g, when saturating in the concentration of 100 mg/L Cd. Meanwhile PPM showed better adsorption capacity comparing to that of PP, indicating some anti interference property of MO, in the coexistence of 0.1 mol/L NaCl. XPS showed that 67% of the cadmium adsorpted by MO, while 33% of cadmium adsorbed by PP, which is mainly based on combination of the Donnan principle (cations pre-concentration effect of PP) and strong specific adsorption effect of MO to cadmium. Pakchoi Seed Germination and growth experiment and leaching experiment were conducted through simulating a soil condition in which PPM exist to explore its adsorption effect of cadmium in penetrating solution and influence on germination and growth of pakchoi. The results showed that wet/dry cyclic and wet sets of leaching experiment both adding PPM possess of almost same adsorption efficiency, with that of 90% and 91% respectively. The pakchoi bud length (2.0 cm) cultivated with 100 mg/L solution adding PPM was much higher than that of control group (0.9 cm) without adding PPM, indicating the compound material could effectively purify osmotic solution containing heavy metal cadmium in soil, solidify heavy metal in soil saturate solution and also prevent heavy metal from transferring to plants.In the practical application, the concentration of calcium ion in soil solution is 103-105 times higher than that of cadmium, seriously interfering with cadmium fixation function. Through the simulation and calculation of Materials Studio software, amino has some selective adsorption ability to cadmium ion. In order to improve the effect of selectivity of cadmium ion with materials, acrylamide monomer (AN) was added into with ratio of 1:1 between propylene amine and acrylic acid, forming plasma multimers carrying nano hydrous manganese oxide complex (PPM-NH2), meanwhile some research relative to its effect of cadmium adsorption in interference of calcium ion was conducted. The results showed in the different calcium concentration interference the adsorption efficiency of PPM-NH2 was higher than that of PPM. In the existing of concentration of 2 mol/L calcium and 100 mg/L cadmium solution, the removal of PPM-NH2 was 17.6% and that of PPM was 3.8%. In the existing of concentration of 0.2 mol/L calcium and 1 mg/L cadmium solution, the removal of PPM-NH2 was 26.4% and that of PPM was 15.1%. And the effects of different organic acids and competitive cations concentration on cadmium adsorption were explored. Except for humic acid, PPM-NH2 adsorption efficiency gradually decreased with increase of organic acid concentration. And in the same molar concentration, interference of salt ions ability on adsorption ranked as Ca2+>Mg2+>Na+. Meanwhile, the experiment of seed germination revealed that the material PPM-NH2 possess higher salt-resistant than PPM existing in circumstance of 0.01 mol/L Ca and 1 mg/L Cd ion. |
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