广西大厂巴里碳酸盐型尾矿的酸化特征及机理

Acidification characteristics and mechanism of carbonate-type tailings of Bali tailings storage,the Dachang tin-polymetallic orefield,Guangxi

以一个堆放近20年的碳酸盐型尾矿的垂向剖面作为研究对象,采用综合地质-地球化学分析方法,包括尾矿组构及组分分析、X衍射分析以及Sobek-ABA估算和NAG测试等,探讨这类尾矿酸化的地质-地球化学特征及酸化作用机理,获得如下认识:①该尾矿剖面由下至上,随着氧化程度的增强,其酸化作用也逐步增强,呈现出明显的层带结构,即下部C层(还原带及原生带)为未蚀变松散尾砂,中部B层(次氧化带及碱缓冲带)为蚀变松散尾砂层,上部A层(氧化带及酸化带)呈厚约100～150cm的板结硬化层;在A层与B层之间形成一个酸化-碱缓冲界面;而氧化-还原界面则较低,位于B层底部接近C层顶部位置。②碱缓冲作用发生在B层内,方解石为碱质的主要来源。③该尾矿的酸中和有效率约为80%,这可能归因于尾矿酸化所产生的次生纤铁矿、石膏等包裹残余方解石,阻断了中和反应的进行。因此,即便是富含碱性碳酸盐的金属硫化物矿尾矿仍然存在酸化污染的可能性。

This paper deals with a weathering profile of carbonate-type tailings （sulfide-bearing carbonate-rich railings） in Bali tailings storage of the Dahang tin-polymetallic orefield in Guangxi. The storage was closed about 20 years ago. Based on studying the profile using composite geological-geochemical methods such as investigation of fabrics and contents, XRD analysis, Sobek-ABA and NAG test, the authors have reached the following conclusions： （1） oxidation of railings increased from bottom to top of the profile, associated with gradually increasing acidity of tailings, resulting in a layering （zoning） structure： C layer at the bottom was a reduction and primary zone （incoherent railings without alteration） ; B layer in middle profile was a suboxidation and base-buffer zone （ incoherent railings with partial alteration） ; A layer at the top was a oxidization and acidification zone （coherent hardpan, 1- 1.5 m in thickness）. An acidic-base buffer interface was located between A layer and B layer, higher than the oxidation-reduction interface at the bottom of B layer. （2） Acidic-base bufferingoccurred in B layer, and the base materials were mainly derived from calcite. （3） Neutral efficiency （or real-con- sumption rate） of carbonate （CaCO3） was about 80%. These phenomena might be attributed to the following reasons： the armor formed by secondary minerals such as lepidocrocite and gypsum during the acidification of tailings caused the development of the rest of carbonate particles and then blocked the neutral reaction of carbonate in tailings. Therefore, it is inferred that the metal-sulfide railings, even if containing excessive carbonate （base materials）, still possess a potential of acidifying and generating acid mine drainage.