The Research On Method Of Polymetallic Nodules And Cobalt Rich Crusts Digested By Ammonium Bifluoride Or Hydrogen Peroxide

Polymetallic nodules and cobalt rich crusts in the ocean contain a quantity of valuable elements such as manganese, cobalt, nickel, copper and others. The mass in the ocean is equivalent to tens to thousands of times than it in the land. Therefore, it is becoming to be a hot research topic. At present, the chemical analysis methods of polymetallic nodules are very complex. It is a great deal of work if the multi-elements of polymetallic nodules are required to be detected in one process.The paper focuses on the digestion methods of nodules and crusts. The main digestion reagent is ammonium hydrogen fluoride or hydrogen peroxide. The instruments of heating are electric oven, microwave digestion instrument and electric hot plate. Sample solution has been determined by ICP-MS and ICP-OES. The results have been discussed to get the effect of digestion. The study will provide data support for establishing an efficient simultaneous analysis method for multi-elements. The main research results as follows:1. A kind of chemical digestion technique has been developed for multi-elements analysis of polymetallic nodules and cobalt rich crusts, which digested by ammonium bifluoride, redigested by hydrochloric acid and tested simultaneously by ICP-MS/ICP-OES online. The entire experimental process time is greatly shortened. And the recoveries of Mn, Fe, Co, Ni and HREE are more than 90%. The detection limits of Ti, V, Cr, Mn, Ni, Cu, Zn, As, Mo are 2.15～47.4μg·g-1, the others’are 0.003～0.881 μg·g-1. The precision (RSD, n=3) is lower than 5%.2. After digested by hydrogen peroxide, nitric acid and hydrochloric acid, samples are detected without acid-driving and redigesting. The result shows that the recoveries of Mn, Fe, Ni, Cd,HREE, Bi, U are more than 90%. The detection limits of this method of Ti, V, Mn, Ni, Cu, Zn, As, Sr, Sn, Sb, Ba are 1.067～29.53μg·g-1, the others’ are 0.010～0.621μg·g-1. The precision (RSD, n=3) of Cr, Ga, Nb, Sb, W are more than 10% and the others’are lower than 10%.3. In this paper, two problems that the results of ICP-MS are increasing with the declining internal standard concentration and the ICP-OES blank values are negative are studied. Diluting the sample solution, reducing the measured amount each time, calculating by error correction formula and using a standard solution which is more appropriate instead are helpful for the problems. 4. Although the digestion speed of microwave is fast, the result is not stable. So it is not a reliable heating method to completely digest the polymetallic nodules and cobalt rich crusts accurately.