Studies On Rapid Purification Techniques Of Cadmium Polluted Irrigation Water

It is well known that Cadmium(Cd) has strong biological toxicity, and Cd pollution of farmland area is expanding in China. Irrigation with Cd contaminated water is one of important sources to lead to high risk for safety of agricultural products and human health risk in paddy soil. So, the development of purification technique is of great significance for Cd contaminated irrigation water, include purification materials and device design. Four materials that red mud particles, limestone, zeolite and rape straw were selected as cost effective large-size porous adsorbent, to optimize the combination of materials was studied by the Cd isothermal adsorption and dynamic simulation experiment, and studied the purification effects of pH and ionic strength. New materials with high protein-SH was created as obligate purify substrate for Cd in irrigation water. New Cd purification device for Cd contaminated irrigation water was created and tested by simulation field irrigation. This paper innovation points are as follows:1. The Cd adsorption performance of four materials for Cd in irrigation water was in the order as limestone > zeolite > red mud particle > rape straw.2. The Cd adsorption by limestone, zeolite and red mud particle from irrigation water is affected by ionic strength which increases with the increase of Cd concentration in balance solution. And the ionic strength in simulated solution has little influence on the purification performance of rape straw.3. The change of pH in the process of purification was studied. In purification process, all four materials are able to raise the pH of irrigation water and are in the order as red mud(by about 4.70 units) > limestone(by about 1.40 units) and zeolite(by about 1.30 units) > rape straw(by about 0.86 units).4. The purifying device for Cd polluted irrigation water was created with high flow-rate, easy to control and low cost. The capacity of purifying device was Cd 24.8~39.7 g, is expected to deal with 439.4~702.2 m3 of Cd polluted water, meet the demand of 1.8~2.8 mu of paddy water purification(irrigation water 3750 m3.ha-1 with Cd 60 ug.L-1; Cd purification concentration of 10 ug.L-1).5. Two kinds of obligate purify Cd substrate with high SH-protein A-PM and T-PM was created with high Cd adsorption capacity. Simulated irrigation water ion fraction, Cd equilibrium adsorption capacity(Mv) of 2 types of modified protein material was in order as T-PM 1678.0 g.m-1>A-PM 1031.9 g.m-1; Cd dynamic adsorption amount(N0) was in order as T-PM 3310.8 g.m-1>A-PM 2097.0 g.m-1. The A-PM and T-PM had less influence on natural component of irrigation water, and could increase solution pH by about 1.56 units.6. Simple and baking-free scheme for the granulation of red mud was created. Mass ratio of solid components is that red mud(60 mesh) of 100~120 copies, diatomite of 15~20 copies. The binder is PUA water solution with volume concentration of 30%, and the mixing ratio of solid components and binder is 100 mL: 20 g.