Gold ore cyanide heap leaching waste

General Procedure gold heap leaching are: sodium cyanide solution as the alkaline leaching solution; Recovery of gold from the leaching solution is typically activated carbon adsorption - desorption, electrolysis; meal replacement, or using speech. The pollution generated by the two processes is basically the same, and some of the pollution of the wastewater is quite different.

First, wastewater

In the gold ore heap leaching process using activated carbon adsorption-desorption and electrolysis, according to the flow path of the solution, three relatively independent and interconnected closed-circuit cycles are included. These three closed loops are as follows:

First, the wastewater produced by the leaching-adsorption tail liquid cycle.

Second, the wastewater generated by the desorption-electrolysis cycle.

Third, the wastewater generated by the closed loop of the heap washing water.

Among the three kinds of wastewater, the composition of the third type of wastewater is simple, and the concentration of the toxic component is the lowest, and it can generally be directly discharged or reserved for the preparation of the leaching solution. The second type of wastewater is the least, and the poison composition is like the first type of wastewater, but the concentration is slightly lower. Depending on the situation (such as the distance between the desorption electrolysis facility and the heap leaching field, etc.), it is determined whether to use separate treatment or return to the heap leaching field to prepare the leaching solution. For liquid use. The first type of wastewater has the largest volume and the strongest toxicity, and is the main body of gold ore heap leaching wastewater, which is the main object to be treated.

Since sodium cyanide is a strong leaching agent, it not only reacts with gold but also reacts with many heavy metals. Therefore, the pollutants in the wastewater, besides cyanide, depend on the mineral type of the ore to be heap leached. . When ore containing heavy metals or arsenic compounds, the corresponding arsenic and heavy metal ions in waste water inevitably produced. The long-term recycling of the adsorption tail liquid leads to the production of thiocyanate (CNS ^- ), cyanate (CNO ^- ), ammonium salt (NH ₄ ⁺ ) and the like in the tail liquid.

Zinc powder to flow in terms of displacement method, it includes only two waste cycle, eliminating the aforementioned second cycle of wastewater generated. Because the process of zinc powder replacement combines the first cycle with the tail liquid produced by the second cycle.

The wastewater in the heap leaching field using the zinc powder replacement method must introduce heavy metal ions, because whether the immersed ore contains heavy metal elements, the process itself requires the addition of a large amount of zinc powder and a small amount of lead compounds. Moreover, zinc powder is mostly industrial products, and itself contains elements such as copper , lead, cobalt , and nickel . The Landusk mine in the United States uses zinc powder replacement method, and its wastewater composition is representative, as shown in the table below.

Table Wastewater composition of the Landus Fund mine leaching site (mg∕L)

Anti-scaling agent - polyacrylate, 5 × 10 ^-6 .

It can be seen from the above table that the components that pollute the environment by wastewater are mainly cyanide, followed by heavy metals such as Cu, Zn, etc. In addition, the pH value and chemical oxygen demand of wastewater from gold ore heaps often do not meet the emission indicators.

The mercury and arsenide content in the above table is not high because the ore is basically free of these two elements. When the heap leaching ore contains arsenopyrite and mercury, the content of arsenic or mercury in the wastewater may reach the allowable value. Dozens of times, even hundreds of times, such as the heap of immersion in the Maquan gold deposit in Gansu, the arsenic content in the leachate reaches hundreds of milligrams per liter. The mercury content in the wastewater from the Dansai gold mine in Guizhou is also very high.

Of cyanide, CN not only free state ^- is present, when the heavy metal wastewater and ferrous ions is present, these ions combine with cyanide ions into the complex, especially iron cyanide complex ion binding, stability Strong, will bring some difficulties to the treatment of cyanide-containing wastewater.

Both ammonium salts and nitrates in wastewater are detrimental to the environment. They are mainly produced by oxidative degradation of cyanide or photolysis by ultraviolet light (sunlight). NH ₄ ^{+ is} first formed, and then oxidized to form nitrite, which is then oxidized to form nitrate.

Second, waste residue

The waste slag of the gold mine heap leaching, including the waste ore after the leaching end plus the hypochlorite solution washing; and the precipitated solids produced during the wastewater treatment and heap leaching process.

Since the gold ore heap is immersed in an alkaline medium, the leaching agent adopts sodium cyanide which is easily oxidatively degraded under natural conditions; after the ore is immersed, it is basically mainly in the form of massive or granular, and the plasticity is poor, thus stability. Ok, so unless there are special circumstances (such as flash floods, large landslides, etc.), it will not pollute the environment as much as wastewater. The sediment generated during the heap leaching process and the wastewater treatment process is also basically a solid form of calcium carbonate, which is very small compared to the ore and is very stable unless it is exposed to acid.

The main pollutant in the solid waste is cyanide remaining in the pores of the waste. Its toxicity is very large in the near future, but it is rapidly degraded under the irradiation and oxidation of sunlight and air. Therefore, its long-term potential hazard is Not big.

The environmental pollution of gold mine heap leaching residue is not mainly due to its chemical toxicity, but because of accidents or poor management, causing waste residue to rush into the river, causing river channel blockage and rushing into farmland, leading to the destruction of crops. In the dry and windy seasons, waste slag yards often become the source of wind sand, which is also a potential threat to farmland.

High Strength Steel Bolts

Ultra high strength heat treated anchor steel bar is a high performance steel that is inductively heat treated from hot rolled steel bars. It is widely used in anchoring, supporting, reinforcement and other projects in coal mine roadways, highway slopes, tunnels, dams, urban foundation pits etc. Pre-stressed concrete works, especially in coal mines.