Alkali slag treatment technology

There isn’t a good way to deal with it. Domestic and international treatment processes for alkali slag can be basically divided into two major categories: the neutralization method and the oxidation method. Neutralization method: includes sulfuric acid acidification, CO2 acidification, and H2S acidification. The Guangzhou Petrochemical Refinery uses the CO2 exhaust gas emitted by the ammonia synthesis unit to neutralize the alkali slag ； Zhenhai Refining & Chemical uses the sulfuric acid acidification method to treat alkali slag while recovering naphthenic acid and crude phenol. These methods alleviate the pressure associated with the treatment of alkaline slag to some extent, but they all cause serious secondary pollution, such as foul odors and highly acidic wastewater during neutralization. Due to the still-high level of pollutants after treatment, these systems often experience stress. Moreover, such processes cause severe equipment corrosion and result in low-quality by-products; as a result, the operational rate of these systems is low, and most of them remain idle. It can basically be considered a type of alkali slag treatment process that has been or is being phased out. Oxidation method: Under certain temperature and pressure conditions, an oxidizing agent is directly mixed with the alkaline slag to oxidize and decompose some of the substances contained in it. Oxidation methods can be divided into chemical reagent oxidation, catalytic oxidation, and air oxidation. The chemical oxidation method uses chlorine gas, hydrogen peroxide, or Fenton’s reagent as oxidants. The characteristic of this type of process is its simple operation and excellent efficiency (removal rates of COD and total sulfur content >95%), but the operating costs are too high. The Taoyuan Refinery in Taiwan has developed an industrial facility for treating refinery alkaline slag using Fenton’s reagent; to date, no industrial installation for treating refinery alkaline slag via chemical oxidation has been used in China. Catalytic oxidation method (CWAO): A fixed-bed reactor is generally used, along with efficient and stable catalysts; air is employed as the oxidant to oxidize the waste alkali sludge under specific temperature and pressure conditions. CWAO performs very well: it achieves a COD removal rate of around 80%, a sulfur removal rate of 99.9%, and it is also capable of converting the nitrogen in ammonia and nitrogen-containing organic compounds into nitrogen gas. CWAO is a promising technology for treating high-concentration waste alkaline solutions, but at present, the use of this technology to handle alkali sludge from refineries is mostly at the laboratory stage both domestically and internationally, with no reports of industrial-scale installations in operation. Air oxidation method: Depending on the oxidation pressure, the air oxidation method is further divided into three types: low-pressure method (LOPROX), moderate-pressure wet oxidation method, and high-pressure wet oxidation method (the Zimpro process in the United States). The air oxidation process technology is the one that achieves the best practical treatment results, operates in the most efficient manner, and is increasingly widely adopted for application. In particular, the moderated wet oxidation process or the medium-high pressure wet oxidation process is basically the preferred process technology for newly installed alkali slag treatment facilities.

Can such a high salt content be handled by the mild wet oxidation process or the medium-high pressure wet oxidation process?