Investigation of Zinc adsorption in paddy and non-paddy soils: a perspective on soil particles mineralogy

  Zinc (Zn) is one of the micro elements, that it’s essential for humans, animals and plants growth at low concentration. High concentrations of heavy metals in soils may constitute long-term health risks to ecosystems and humans. Clay minerals play an important role in accumulation, adsorption/desorption, as well as exchange processes of metal ions. The bio avaibility of these trace elements by plants decreases with the clay mineral content in soils, referring to the strong retention capacity of clay minerals to zinc. The aim of this study is to evaluate zinc sorption by soil fractions in puddling and non-puddling condition and it’s relation with mineralogy. According to previous studies, eight profiles (Four in paddy and four in non-paddy condition) were sampled and described and all soil profiles were classified in Inceptisols order. For this research, eight surface soil samples (0-30 cm) were collected. Soil samples were air-dried and crushed to pass through a 2-mm sieve for further laboratory analysis and physico-chemical experiments was performed. All size fractions were separated and content of minerals in sand, silt and clay fraction was determined. Zinc sorption analysis was performed by adding eight rates of zn from 100 to 3000 µmol in 0.01M solution as background to sand, silt and clay particles and shaken for 24 h. The data obtained for zinc sorption on different samples was analyzed for Freundilch, Langmuir and Temkin equations. Results of study showed that the amount of zinc sorbed increased with increasing in the concentration of zn in the contact solutions. Zinc sorption was very much in the clay and silt fraction rather than sand fraction. The results showed that freundlich equation (R2=0.95) more fit than others equations, in puddling and non-puddling condition. KF of Freundilch, indicating sorption value in equilibrium concentration of Zn that in clay fraction of puddling soils it’s mean (9668.5) more than silt (4682.7) and sand (2666) fractions. KF Mean of Freundilch in clay, sand and silt particles of no puddling soils is equal to 8313, 5982.7 and 2991.7 respectively. Results indicated sorbed Zn value was significantly correlated with clay content in all sample (n=8, r= 0.73*). The presence vermiculite mineral in puddling soils is cause for high Zn sorption (n=8, r2=0.768*), whereas semectite and palygorskite minerals in no puddling soils affected on Zn sorption( n=8, r= 0.85*). In silt fraction mixed minerals such as illite-vermiculite, and illite-smectite (n= 8, r= 0.77*) and low content of calcite are main factors to zinc sorption. The presence of quartz and feldespare in sand fraction induce to low sorption of zinc. But the presence rarely of calcite and dolomite (n= 8, r= 0.96*) in this fraction increase zinc sorption value. Generally, concluded that minerals type in soil particles are main factors to element sorption. The presence of vermiculite and smectite minerals in paddy soils and non paddy soils are important clay minerals in Zn sorption.