Study On The Mechanisms Of Proton Exchange And Mn²+release For δ-MnO₂in Water

δ-MnO₂is one of the main manganese oxide minerals which has the great adsorption andoxidation capacity for heavy metals such as Cr（III）, Co（II）, and Pb（II）. It plays an important rolein regulating the transformation and distribution of heavy metals in water. However the effect onenvironment from itself is received more and more emphases. Systemic investigation on theenvironment behavior of δ-MnO₂itself is both academic and practiee.First the objective of this study was to investigate the effect of different environmental factorson the surface proton exchange and Mn（2+）release processes from δ-MnO₂which prepared by ourrenovated hydrothermal method and further propose the possible mechanisms. Then multivariateanalysis of the effect was studied by orthogonal methods. The main results as follows:（1） The effects to environmental behavior of the δ-MnO₂on electrolytes and ion strength weredifferent. There is significantly negative correlation between amount of Mn（2+）release and ionstrength. The negative relevant we assumed was due to lower activity coefficient at higher ionstrength. Along with the increasing of Na+, H of hydroxyl on the surface was exchanged withNa+and then released to solution. In addition, cations have more effects than anions in differentelectrolytes.（2） In the range of this experiment, the initial values of pH which influence electrostaticpotential and surface charge of δ-MnO₂have a great effect. In contrast, temperature has a lesseffect on release behavior.（3） Absorption of heavy metals (Pb²⁺, Cr³⁺or Co²⁺) on δ-MnO₂by different mechanismscaused different amount of Mn（2+）released，the influence order of these three heavy metals onMn²⁺released at the same concentration was as follows: Cr³⁺＞Co²⁺＞Pb²⁺. On the contrary,Pb²⁺has the greatest effect than Cr³⁺and Co²⁺and mainly promoted H+release.（4） With the method of orthogonal experiment, we can obtain the effect weight of each factorfor trial result. By combining the single factors temperature and pH, results showed that pH wasthe dominant factor. In the presence of three heavy metals, they mainly affect the amounts ofMn（2+）release even under different initial pH values. But the amounts of surface proton exchangewas both related to initial pH and metal ions. The stability of metal ion-EDTA complex alsoinfluenced the environmental behaviours of δ-MnO₂...