Nitric Acid Extraction of Phosphorus from Sewage Sludge Ash
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Solution Overview
Problem
Current methods for extracting phosphorus from incinerated sewage sludge ash (ISSA) face challenges such as high production costs, inefficient phosphorus recovery, and environmental concerns due to the use of sulfuric acid and hydrochloric acid, as well as complex operation procedures and potential heavy metal leaching, which hinder the development of a complete process flow for producing N-P compound fertilizers.
Innovation Solution
A method involving the use of nitric acid to extract phosphorus from ISSA, followed by pH adjustment with aqueous ammonia, which results in a high recovery rate and cost-effective production of N-P compound fertilizers, incorporating a simple operation process and minimizing waste generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If sulfuric acid or hydrochloric acid is used to extract phosphorus from ISSA, then phosphorus extraction can be achieved, but production costs increase and environmental harm increases
Solution Approach 1:
The patent changes the chemical parameter by using nitric acid instead of sulfuric or hydrochloric acid, and controls the extraction temperature within 0-100°C. This parameter change eliminates the formation of harmful gypsum and reduces metal leaching, thereby reducing environmental harm and production costs while maintaining phosphorus extraction efficiency
Solution Approach 2:
The patent converts the potentially harmful effect of acid extraction into a beneficial process by using nitric acid, which oxidizes phosphorus to phosphoric acid for efficient extraction, while avoiding the harmful side reactions of sulfuric and hydrochloric acids. The method turns a potentially polluting extraction process into an environmentally friendly one
2Quantity of substance
If high liquid-to-solid ratio is used in wet chemical extraction, then phosphorus extraction is improved, but waste liquid increases and operating costs increase
Solution Approach 1:
The patent optimizes the liquid-to-solid ratio parameter and extraction temperature parameter to achieve efficient phosphorus extraction with minimal liquid usage. By controlling temperature within 0-100°C and adjusting the liquid-to-solid ratio, the method maximizes phosphorus recovery while minimizing waste liquid generation and operating costs
3Quantity of substance
If complex operation procedures are used in phosphorus extraction, then extraction completeness is improved, but production cost increases
Solution Approach 1:
The patent segments the phosphorus extraction process into distinct stages: (1) acid treatment and filtration to separate phosphorus-rich supernatant from residue, (2) pH adjustment to precipitate phosphorus, and (3) filtration and drying. This segmentation simplifies each step while maintaining high phosphorus recovery rate
Solution Approach 2:
The patent uses pH adjustment as an intermediary step that converts soluble phosphoric acid into insoluble phosphorus precipitate. This intermediary transformation simplifies the separation process and improves phosphorus recovery without requiring complex operation procedures
4Quantity of substance
If struvite crystallization or vivianite recovery method is used, then phosphorus recovery is achieved, but recovery rate decreases due to strict operating condition requirements
Solution Approach 1:
The patent changes the operating parameters by using nitric acid extraction followed by pH adjustment to a specific range (2-11), which creates optimal conditions for phosphorus precipitation. This parameter optimization achieves high recovery rates without the strict operating condition requirements of struvite or vivianite methods
Solution Approach 2:
The patent uses a simple, cost-effective pH adjustment process with readily available reagents to achieve phosphorus recovery, replacing complex and expensive crystallization processes. The method uses common chemicals and simple equipment, making it economically viable with high recovery rates
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively recovers phosphorus with a high yield, reduces production costs, and produces a fertilizer with multiple nutrients, suitable for agricultural applications while minimizing environmental impact.
Implementation Method 1
heating and mixing a nitric acid solution with the ISSA to obtain a mixed solution
Implementation Method 2
adjusting the phosphorus-rich supernatant to a pH value of 6 to 8 using aqueous ammonia
Implementation Method 3
conducting a reaction fully under stirring to obtain a white turbid liquid, and conducting centrifugation on the white turbid liquid to avoid formation of colloids, thereby obtaining a white precipitate
Implementation Method 4
conducting centrifugation on an obtained reacted mixed solution to avoid formation of colloids, thereby obtaining a phosphorus-rich supernatant and an ISSA residue
Data Source
AI summary
The present disclosure provides a method for preparing an N-P compound fertilizer from incinerated sewage sludge ash (ISSA), and relates to the technical field of compound fertilizer production. In the present disclosure, the ISSA is used as a main raw material, and a phosphorus-rich supernatant is obtained using high-concentration nitric acid at a low liquid-to-solid ratio. The phosphorus-rich supernatant and aqueous ammonia are mixed to obtain a white precipitate. The white precipitate is dried and pulverized to obtain a high-grade N-P compound fertilizer. The present disclosure realizes the resource utilization of excess sludge in sewage treatment plants.