CN102101732A - Method for recovering hydrazine sulfate and chromium hydroxide from chromium-containing waste acid - Google Patents

Abstract

The invention discloses a method for recovering hydrazine sulfate and chromium hydroxide from chromium-containing waste acid, which comprises the following steps of: diluting hydrazine hydrate, slowly adding waste acid into the hydrazine hydrate with stirring, ensuring an acid adding end point when the pH of feed liquid is 0.8-1.2, and reacting hexavalent chromium in the waste acid with the hydrazine hydrate to reduce the hexavalent chromium into trivalent chromium and generate indissoluble hydrazine sulfate crystals; performing solid-liquid separation to obtain crude hydrazine sulfate and acidic chromium sulfate solution; adding alkali into acidic chromium sulfate solution for neutralization to obtain a chromium hydroxide precipitate, performing solid-liquid separation, washing with water, and drying to obtain an industrial product chromium hydroxide meeting quality requirement; and treating wastewater subjected to solid-liquid separation and washing in a wastewater treatment device for up-to-standard emission. The method is easy to operate, and the chromium-containing waste acid is treated for up-to-standard emission; meanwhile, the hydrazine sulfate and chromium hydroxide are recovered, so that the resources are reasonably utilized and the economic benefit is obvious.

Description

A kind of from contain the chromium spent acid method of reclaim(ed) sulfuric acid hydrazine and chromium hydroxide

Technical field

The present invention relates to contain the improvement and the resource recycling of chromium spent acid.

Background technology

Vat Red 31 is a kind of important dyestuff, but in it is produced, only could guarantee that with the sexavalent chrome oxidation coloured light is accurate in the strongly-acid medium, thus, produce a large amount of spent acid, about 10 tons/ton, the about 55-68% of acidity contains organism about 0.5%, it is about 3% to contain total chromium, wherein, contains sexavalent chrome about 0.6%.

This spent acid becomes Hazardous wastes owing to contain chromium, and it is three prices that current enterprise takes to add earlier the S-WAT reduction of hexavalent chromium, adds the alkali neutralization again, and the method that generates chromium hydroxide and reclaim need expend a large amount of alkali, produces a large amount of brine wastes simultaneously, and processing cost is difficult to bear.

This contains the chromium spent acid also can hydro-oxidation barium or bariumchloride, generates barium sulfate precipitate, continues to add alkali after the separation again and generates chromium hydroxide.But it is lower that barium sulfate is worth, so this method does not have the industrial implementation meaning.

Summary of the invention

The present invention proposes and a kind of this spent acid is handled the method for making hydrazonium sulfate and chromium hydroxide, with reclaim(ed) sulfuric acid and chromium.

Technical scheme of the present invention is as follows:

A kind of from contain the chromium spent acid method of reclaim(ed) sulfuric acid hydrazine and chromium hydroxide, it comprises the steps:

(1) hydrazine hydrate being diluted to mass percentage concentration is the aqueous solution below 20%, after will containing the chromium spent acid and removing solid impurity after filtration, under agitation slowly join in the hydrazine hydrate, control adds the pH=0.8-1.2 of sour terminal point to feed liquid, sexavalent chrome in the spent acid and hydrazine hydrate reaction, be reduced into trivalent chromium, generate the hydrazonium sulfate xln of indissoluble simultaneously;

(2) solid-liquid separation obtains thick hydrazonium sulfate and acid chromium sulfate solution;

(3) with thick hydrazonium sulfate through recrystallization, the industrial goods hydrazonium sulfate that obtains conforming to quality requirements;

(4) the oxytropism chromium sulfate solution adds alkali, and neutralization generates chromium hydroxide precipitation, and solid-liquid separation washes after drying with water, promptly obtains the industrial goods chromium hydroxide that conforms to quality requirements;

(5) send wastewater treatment equipment to handle back qualified discharge (wastewater treatment is an ordinary method, not in present method scope) step 4 solid-liquid separation and washes.

The inventive method is simple to operate, has both administered to contain the chromium spent acid, makes its qualified discharge, has reclaimed hydrazonium sulfate and chromium hydroxide simultaneously, makes resource obtain reasonable utilization, and economic benefit is obvious.

Embodiment

Further specify technological process of the present invention below by embodiment.

Embodiment:

Getting mass percentage concentration is that 40% hydrazine hydrate 49.5mL is diluted to 20% solution, get 40mL and contain chromium spent acid (acidity 65%) filtration, under agitation slowly be added drop-wise in 20% hydrazine hydrate solution, dropping time 2h, control adds sour terminal point material liquid pH=0.8, generate white crystalline hydrazonium sulfate precipitation, reaction formula is as follows:

NH ₂-NH ₂·H ₂O+H ₂SO ₄=?NH ₂-NH ₂·H ₂SO ₄

2Cr ₂O ₇ ^2-+4H ⁺+3N ₂H ₄·H ₂O→4Cr(OH) ₃+N ₂+5H ₂O

2Cr(OH) ₃+3H ₂SO ₄→Cr ₂(SO4) ₃+6H ₂O

Leave standstill 0.5h, put into 2h in 5 ℃ the refrigerator then.

Filter, with a small amount of cold clear water (5 ℃) washing hydrazonium sulfate filter cake, filtrate merges in the synthesis mother liquid.Get the 155mL clear water and be heated to 60 ℃ (27.65g/100g, 60 ℃), will wash back hydrazonium sulfate filter cake and add stirring and dissolving, cooling, crystallization merges in crystalline mother solution and the synthesis mother liquid.

Hydrazonium sulfate oven dry behind the recrystallization, analyzing its content is 98.1%, gets hydrazonium sulfate 42.25 g, calculates with this, the vitriolic rate of recovery is about 78%.

Under agitation, in crystalline mother solution and synthesis mother liquid amalgamation liquid, drip 30%NaOH, about control pH=7.5, generate the sap green chromium hydroxide precipitation, continue to stir 0.5h, leave standstill 0.5h, filter, filter cake is with a small amount of clear water washed twice, washing water and mother liquor merge, through the diphenyl carbazide spectrophotometry analysis, total chromium concn is 0.38mg/L, goes wastewater treatment.

Chromium hydroxide precipitation drying, content are 92.4%.

Claims (1)

1. the method for reclaim(ed) sulfuric acid hydrazine and chromium hydroxide from contain the chromium spent acid is characterized in that it comprises the steps:

(1) hydrazine hydrate being diluted to mass percentage concentration is the aqueous solution below 20%, after will containing the chromium spent acid and removing solid impurity after filtration, under agitation slowly join in the hydrazine hydrate, control adds the pH=0.8-1.2 of sour terminal point to feed liquid, sexavalent chrome in the spent acid and hydrazine hydrate reaction, be reduced into trivalent chromium, generate the hydrazonium sulfate xln of indissoluble simultaneously;

(2) solid-liquid separation obtains thick hydrazonium sulfate and acid chromium sulfate solution;

(3) with thick hydrazonium sulfate through recrystallization, the industrial goods hydrazonium sulfate that obtains conforming to quality requirements;

(4) the oxytropism chromium sulfate solution adds alkali, and neutralization generates chromium hydroxide precipitation, and solid-liquid separation washes after drying with water, promptly obtains the industrial goods chromium hydroxide that conforms to quality requirements;

(5) send wastewater treatment equipment to handle the back qualified discharge step 4 solid-liquid separation and washes.