Study On Phase Transition Law Of Pre-reduction Process Of Deep-sea Manganese Nodules

Deep-sea manganese nodules have rich metal elements such as Fe,Mn,Cu,Co,Ni,etc.,which have great potential economic value and broad comprehensive utilization prospects.Reasonable classification and extraction of various valuable elements are beneficial to alleviate the increasingly tense mineral resources in the land.In this paper,deep-sea manganese nodules were used as raw materials,and its basic mineral characteristics were analyzed.Graphite powders were used as reducing agent to investigate the characteristics of pre-reduction process of nodules.The experiments explored the migration of Fe,Mn,Ni,Cu and Co during the pre-reduction of nodules,aiming to provide basic data support for the pre-reduction of nodules in rotary kiln.The mineralogical basic characteristics of deep-sea manganese nodules have shown that nodules had various forms such as grape-like,ellipsoidal,tumor-like,oblate-shaped,cauliflower,etc.Generally,nodules are 1-4 cm in diameter.It has a three-layer structure such as an external tuberculosis layer,an internal tuberculosis layer,and a core layer.XRF analysis shows that the contents of Mn,Fe,Ni and Cu in nodules were 41.55%,11.05%,2.22%and 1.66%respectively;the content of Fe in external tuberculosis layer is higher than that in internal tuberculosis layer and core layer,and the content of Mn and Cu is the lowest.In internal tuberculosis layer,the content of Mn and Ni is the highest and the content of Fe was the lowest.In the core layer,the content of Mn,Fe,Ni and Cu is close to that of external tuberculosis layer.The main mineral phases in nodules are birnessite,todorokite,maganosite,?-MnO₂,phillipsite and quartz.The content of mineral phases in different nodules has certain differences.Manganese nodules has good grinding performance.The average particle size of the external tuberculosis layer,the internal tuberculosis layer and the core layer powder are 69.29?m,51.25?m and 57.37?m,respectively.Thermodynamic analysis shows that CuO can be reduced at temperatures above 50°C.NiO,CoO,FeO,etc.can be reduced at temperatures during 400-800°C,and MnO need to be reduced by carbon at temperatures above 1420°C.The oxide of Mn in nodules mainly exist in the form of MnO2,and MnO2 can be converted to low-valent oxides of Mn2O3 and Mn₃O₄ at temperatures above 400°C.Kenetic analysis shows that the pre-reduction of nodules is direct reduction.CO produced and consumed during the process.The entire system consumes carbon,and the conversion rate X of the reaction is related to the reaction time t.Differential thermal analysis shows that during 25-1300°C,the sample mass and the heat flow in the furnace continues to decrease with increasing temperature,and the intense heat release occurs at 50°C,200°C,400°C,960°C and 1100°C,where the reduction or phase transition temperature transition point of the oxide occurs.During 1100-1300°C,when the carbon ratio is 0.2,the weight loss of the sample increases with the increase of temperature from 24.7%to 32.4%after 1 h of reduction.After 2 h of reduction,the weight loss of the sample increases from 25.8%to 44.2%.With the condition of reduction time of 2 h,the metal elements such as Fe,Mn,Cu,Co and Ni are mainly concentrated in the rod or bead material,and the elements such as Si,C and O are mainly present in the slag.The alloy and slag are mixed together.With the increase of temperature,the metal conversion rate of Fe,Mn,Cu and Ni in the sample increases,the conversion rate of Cu and Ni is higher,the conversion rate exceeded 80%and 70%,respectively.After 1 h of reduction at 1300°C,the conversion rate of Mn and Fe can reach about 70%,and the conversion rate is close to 80%after 2 h reduction.During 1100-1300°C,when the carbon ratio is 0.3,the weight loss of the sample increases with the increase of temperature from 24.9%to 33.9%after 1 h of reduction.After 2 h of reduction,the weight loss of the sample increases from 25.8%to 46.2%.The spherical alloy material with high Mn content appeares on the surface of the sample reduced at 1300°C.The presence of the alloy spherical material is beneficial to the separation of alloys from the sample slag.The increase of temperature is beneficial to the increase of metal conversion rate in the sample.The conversion rates of Fe,Mn,Cu and Ni in the sample reduced at 1300°C are 70.52%,72.04%,74.53%and 82.89%,respectively.